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+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+//! A contiguous growable array type with heap-allocated contents, written
+//! `Vec<T>`.
+//!
+//! Vectors have *O*(1) indexing, amortized *O*(1) push (to the end) and
+//! *O*(1) pop (from the end).
+//!
+//! Vectors ensure they never allocate more than `isize::MAX` bytes.
+//!
+//! # Examples
+//!
+//! You can explicitly create a [`Vec`] with [`Vec::new`]:
+//!
+//! ```
+//! let v: Vec<i32> = Vec::new();
+//! ```
+//!
+//! ...or by using the [`vec!`] macro:
+//!
+//! ```
+//! let v: Vec<i32> = vec![];
+//!
+//! let v = vec![1, 2, 3, 4, 5];
+//!
+//! let v = vec![0; 10]; // ten zeroes
+//! ```
+//!
+//! You can [`push`] values onto the end of a vector (which will grow the vector
+//! as needed):
+//!
+//! ```
+//! let mut v = vec![1, 2];
+//!
+//! v.push(3);
+//! ```
+//!
+//! Popping values works in much the same way:
+//!
+//! ```
+//! let mut v = vec![1, 2];
+//!
+//! let two = v.pop();
+//! ```
+//!
+//! Vectors also support indexing (through the [`Index`] and [`IndexMut`] traits):
+//!
+//! ```
+//! let mut v = vec![1, 2, 3];
+//! let three = v[2];
+//! v[1] = v[1] + 5;
+//! ```
+//!
+//! [`push`]: Vec::push
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+#[cfg(not(no_global_oom_handling))]
+use core::cmp;
+use core::cmp::Ordering;
+use core::fmt;
+use core::hash::{Hash, Hasher};
+use core::iter;
+use core::marker::PhantomData;
+use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
+use core::ops::{self, Index, IndexMut, Range, RangeBounds};
+use core::ptr::{self, NonNull};
+use core::slice::{self, SliceIndex};
+
+use crate::alloc::{Allocator, Global};
+#[cfg(not(no_borrow))]
+use crate::borrow::{Cow, ToOwned};
+use crate::boxed::Box;
+use crate::collections::{TryReserveError, TryReserveErrorKind};
+use crate::raw_vec::RawVec;
+
+#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
+pub use self::drain_filter::DrainFilter;
+
+mod drain_filter;
+
+#[cfg(not(no_global_oom_handling))]
+#[stable(feature = "vec_splice", since = "1.21.0")]
+pub use self::splice::Splice;
+
+#[cfg(not(no_global_oom_handling))]
+mod splice;
+
+#[stable(feature = "drain", since = "1.6.0")]
+pub use self::drain::Drain;
+
+mod drain;
+
+#[cfg(not(no_borrow))]
+#[cfg(not(no_global_oom_handling))]
+mod cow;
+
+#[cfg(not(no_global_oom_handling))]
+pub(crate) use self::in_place_collect::AsVecIntoIter;
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use self::into_iter::IntoIter;
+
+mod into_iter;
+
+#[cfg(not(no_global_oom_handling))]
+use self::is_zero::IsZero;
+
+mod is_zero;
+
+#[cfg(not(no_global_oom_handling))]
+mod in_place_collect;
+
+mod partial_eq;
+
+#[cfg(not(no_global_oom_handling))]
+use self::spec_from_elem::SpecFromElem;
+
+#[cfg(not(no_global_oom_handling))]
+mod spec_from_elem;
+
+use self::set_len_on_drop::SetLenOnDrop;
+
+mod set_len_on_drop;
+
+#[cfg(not(no_global_oom_handling))]
+use self::in_place_drop::{InPlaceDrop, InPlaceDstBufDrop};
+
+#[cfg(not(no_global_oom_handling))]
+mod in_place_drop;
+
+#[cfg(not(no_global_oom_handling))]
+use self::spec_from_iter_nested::SpecFromIterNested;
+
+#[cfg(not(no_global_oom_handling))]
+mod spec_from_iter_nested;
+
+#[cfg(not(no_global_oom_handling))]
+use self::spec_from_iter::SpecFromIter;
+
+#[cfg(not(no_global_oom_handling))]
+mod spec_from_iter;
+
+#[cfg(not(no_global_oom_handling))]
+use self::spec_extend::SpecExtend;
+
+use self::spec_extend::TrySpecExtend;
+
+mod spec_extend;
+
+/// A contiguous growable array type, written as `Vec<T>`, short for 'vector'.
+///
+/// # Examples
+///
+/// ```
+/// let mut vec = Vec::new();
+/// vec.push(1);
+/// vec.push(2);
+///
+/// assert_eq!(vec.len(), 2);
+/// assert_eq!(vec[0], 1);
+///
+/// assert_eq!(vec.pop(), Some(2));
+/// assert_eq!(vec.len(), 1);
+///
+/// vec[0] = 7;
+/// assert_eq!(vec[0], 7);
+///
+/// vec.extend([1, 2, 3]);
+///
+/// for x in &vec {
+/// println!("{x}");
+/// }
+/// assert_eq!(vec, [7, 1, 2, 3]);
+/// ```
+///
+/// The [`vec!`] macro is provided for convenient initialization:
+///
+/// ```
+/// let mut vec1 = vec![1, 2, 3];
+/// vec1.push(4);
+/// let vec2 = Vec::from([1, 2, 3, 4]);
+/// assert_eq!(vec1, vec2);
+/// ```
+///
+/// It can also initialize each element of a `Vec<T>` with a given value.
+/// This may be more efficient than performing allocation and initialization
+/// in separate steps, especially when initializing a vector of zeros:
+///
+/// ```
+/// let vec = vec![0; 5];
+/// assert_eq!(vec, [0, 0, 0, 0, 0]);
+///
+/// // The following is equivalent, but potentially slower:
+/// let mut vec = Vec::with_capacity(5);
+/// vec.resize(5, 0);
+/// assert_eq!(vec, [0, 0, 0, 0, 0]);
+/// ```
+///
+/// For more information, see
+/// [Capacity and Reallocation](#capacity-and-reallocation).
+///
+/// Use a `Vec<T>` as an efficient stack:
+///
+/// ```
+/// let mut stack = Vec::new();
+///
+/// stack.push(1);
+/// stack.push(2);
+/// stack.push(3);
+///
+/// while let Some(top) = stack.pop() {
+/// // Prints 3, 2, 1
+/// println!("{top}");
+/// }
+/// ```
+///
+/// # Indexing
+///
+/// The `Vec` type allows to access values by index, because it implements the
+/// [`Index`] trait. An example will be more explicit:
+///
+/// ```
+/// let v = vec![0, 2, 4, 6];
+/// println!("{}", v[1]); // it will display '2'
+/// ```
+///
+/// However be careful: if you try to access an index which isn't in the `Vec`,
+/// your software will panic! You cannot do this:
+///
+/// ```should_panic
+/// let v = vec![0, 2, 4, 6];
+/// println!("{}", v[6]); // it will panic!
+/// ```
+///
+/// Use [`get`] and [`get_mut`] if you want to check whether the index is in
+/// the `Vec`.
+///
+/// # Slicing
+///
+/// A `Vec` can be mutable. On the other hand, slices are read-only objects.
+/// To get a [slice][prim@slice], use [`&`]. Example:
+///
+/// ```
+/// fn read_slice(slice: &[usize]) {
+/// // ...
+/// }
+///
+/// let v = vec![0, 1];
+/// read_slice(&v);
+///
+/// // ... and that's all!
+/// // you can also do it like this:
+/// let u: &[usize] = &v;
+/// // or like this:
+/// let u: &[_] = &v;
+/// ```
+///
+/// In Rust, it's more common to pass slices as arguments rather than vectors
+/// when you just want to provide read access. The same goes for [`String`] and
+/// [`&str`].
+///
+/// # Capacity and reallocation
+///
+/// The capacity of a vector is the amount of space allocated for any future
+/// elements that will be added onto the vector. This is not to be confused with
+/// the *length* of a vector, which specifies the number of actual elements
+/// within the vector. If a vector's length exceeds its capacity, its capacity
+/// will automatically be increased, but its elements will have to be
+/// reallocated.
+///
+/// For example, a vector with capacity 10 and length 0 would be an empty vector
+/// with space for 10 more elements. Pushing 10 or fewer elements onto the
+/// vector will not change its capacity or cause reallocation to occur. However,
+/// if the vector's length is increased to 11, it will have to reallocate, which
+/// can be slow. For this reason, it is recommended to use [`Vec::with_capacity`]
+/// whenever possible to specify how big the vector is expected to get.
+///
+/// # Guarantees
+///
+/// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
+/// about its design. This ensures that it's as low-overhead as possible in
+/// the general case, and can be correctly manipulated in primitive ways
+/// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
+/// If additional type parameters are added (e.g., to support custom allocators),
+/// overriding their defaults may change the behavior.
+///
+/// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
+/// triplet. No more, no less. The order of these fields is completely
+/// unspecified, and you should use the appropriate methods to modify these.
+/// The pointer will never be null, so this type is null-pointer-optimized.
+///
+/// However, the pointer might not actually point to allocated memory. In particular,
+/// if you construct a `Vec` with capacity 0 via [`Vec::new`], [`vec![]`][`vec!`],
+/// [`Vec::with_capacity(0)`][`Vec::with_capacity`], or by calling [`shrink_to_fit`]
+/// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
+/// types inside a `Vec`, it will not allocate space for them. *Note that in this case
+/// the `Vec` might not report a [`capacity`] of 0*. `Vec` will allocate if and only
+/// if <code>[mem::size_of::\<T>]\() * [capacity]\() > 0</code>. In general, `Vec`'s allocation
+/// details are very subtle --- if you intend to allocate memory using a `Vec`
+/// and use it for something else (either to pass to unsafe code, or to build your
+/// own memory-backed collection), be sure to deallocate this memory by using
+/// `from_raw_parts` to recover the `Vec` and then dropping it.
+///
+/// If a `Vec` *has* allocated memory, then the memory it points to is on the heap
+/// (as defined by the allocator Rust is configured to use by default), and its
+/// pointer points to [`len`] initialized, contiguous elements in order (what
+/// you would see if you coerced it to a slice), followed by <code>[capacity] - [len]</code>
+/// logically uninitialized, contiguous elements.
+///
+/// A vector containing the elements `'a'` and `'b'` with capacity 4 can be
+/// visualized as below. The top part is the `Vec` struct, it contains a
+/// pointer to the head of the allocation in the heap, length and capacity.
+/// The bottom part is the allocation on the heap, a contiguous memory block.
+///
+/// ```text
+/// ptr len capacity
+/// +--------+--------+--------+
+/// | 0x0123 | 2 | 4 |
+/// +--------+--------+--------+
+/// |
+/// v
+/// Heap +--------+--------+--------+--------+
+/// | 'a' | 'b' | uninit | uninit |
+/// +--------+--------+--------+--------+
+/// ```
+///
+/// - **uninit** represents memory that is not initialized, see [`MaybeUninit`].
+/// - Note: the ABI is not stable and `Vec` makes no guarantees about its memory
+/// layout (including the order of fields).
+///
+/// `Vec` will never perform a "small optimization" where elements are actually
+/// stored on the stack for two reasons:
+///
+/// * It would make it more difficult for unsafe code to correctly manipulate
+/// a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
+/// only moved, and it would be more difficult to determine if a `Vec` had
+/// actually allocated memory.
+///
+/// * It would penalize the general case, incurring an additional branch
+/// on every access.
+///
+/// `Vec` will never automatically shrink itself, even if completely empty. This
+/// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
+/// and then filling it back up to the same [`len`] should incur no calls to
+/// the allocator. If you wish to free up unused memory, use
+/// [`shrink_to_fit`] or [`shrink_to`].
+///
+/// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
+/// sufficient. [`push`] and [`insert`] *will* (re)allocate if
+/// <code>[len] == [capacity]</code>. That is, the reported capacity is completely
+/// accurate, and can be relied on. It can even be used to manually free the memory
+/// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
+/// when not necessary.
+///
+/// `Vec` does not guarantee any particular growth strategy when reallocating
+/// when full, nor when [`reserve`] is called. The current strategy is basic
+/// and it may prove desirable to use a non-constant growth factor. Whatever
+/// strategy is used will of course guarantee *O*(1) amortized [`push`].
+///
+/// `vec![x; n]`, `vec![a, b, c, d]`, and
+/// [`Vec::with_capacity(n)`][`Vec::with_capacity`], will all produce a `Vec`
+/// with exactly the requested capacity. If <code>[len] == [capacity]</code>,
+/// (as is the case for the [`vec!`] macro), then a `Vec<T>` can be converted to
+/// and from a [`Box<[T]>`][owned slice] without reallocating or moving the elements.
+///
+/// `Vec` will not specifically overwrite any data that is removed from it,
+/// but also won't specifically preserve it. Its uninitialized memory is
+/// scratch space that it may use however it wants. It will generally just do
+/// whatever is most efficient or otherwise easy to implement. Do not rely on
+/// removed data to be erased for security purposes. Even if you drop a `Vec`, its
+/// buffer may simply be reused by another allocation. Even if you zero a `Vec`'s memory
+/// first, that might not actually happen because the optimizer does not consider
+/// this a side-effect that must be preserved. There is one case which we will
+/// not break, however: using `unsafe` code to write to the excess capacity,
+/// and then increasing the length to match, is always valid.
+///
+/// Currently, `Vec` does not guarantee the order in which elements are dropped.
+/// The order has changed in the past and may change again.
+///
+/// [`get`]: slice::get
+/// [`get_mut`]: slice::get_mut
+/// [`String`]: crate::string::String
+/// [`&str`]: type@str
+/// [`shrink_to_fit`]: Vec::shrink_to_fit
+/// [`shrink_to`]: Vec::shrink_to
+/// [capacity]: Vec::capacity
+/// [`capacity`]: Vec::capacity
+/// [mem::size_of::\<T>]: core::mem::size_of
+/// [len]: Vec::len
+/// [`len`]: Vec::len
+/// [`push`]: Vec::push
+/// [`insert`]: Vec::insert
+/// [`reserve`]: Vec::reserve
+/// [`MaybeUninit`]: core::mem::MaybeUninit
+/// [owned slice]: Box
+#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "Vec")]
+#[rustc_insignificant_dtor]
+pub struct Vec<T, #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global> {
+ buf: RawVec<T, A>,
+ len: usize,
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Inherent methods
+////////////////////////////////////////////////////////////////////////////////
+
+impl<T> Vec<T> {
+ /// Constructs a new, empty `Vec<T>`.
+ ///
+ /// The vector will not allocate until elements are pushed onto it.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// # #![allow(unused_mut)]
+ /// let mut vec: Vec<i32> = Vec::new();
+ /// ```
+ #[inline]
+ #[rustc_const_stable(feature = "const_vec_new", since = "1.39.0")]
+ #[stable(feature = "rust1", since = "1.0.0")]
+ #[must_use]
+ pub const fn new() -> Self {
+ Vec { buf: RawVec::NEW, len: 0 }
+ }
+
+ /// Constructs a new, empty `Vec<T>` with at least the specified capacity.
+ ///
+ /// The vector will be able to hold at least `capacity` elements without
+ /// reallocating. This method is allowed to allocate for more elements than
+ /// `capacity`. If `capacity` is 0, the vector will not allocate.
+ ///
+ /// It is important to note that although the returned vector has the
+ /// minimum *capacity* specified, the vector will have a zero *length*. For
+ /// an explanation of the difference between length and capacity, see
+ /// *[Capacity and reallocation]*.
+ ///
+ /// If it is important to know the exact allocated capacity of a `Vec`,
+ /// always use the [`capacity`] method after construction.
+ ///
+ /// For `Vec<T>` where `T` is a zero-sized type, there will be no allocation
+ /// and the capacity will always be `usize::MAX`.
+ ///
+ /// [Capacity and reallocation]: #capacity-and-reallocation
+ /// [`capacity`]: Vec::capacity
+ ///
+ /// # Panics
+ ///
+ /// Panics if the new capacity exceeds `isize::MAX` bytes.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = Vec::with_capacity(10);
+ ///
+ /// // The vector contains no items, even though it has capacity for more
+ /// assert_eq!(vec.len(), 0);
+ /// assert!(vec.capacity() >= 10);
+ ///
+ /// // These are all done without reallocating...
+ /// for i in 0..10 {
+ /// vec.push(i);
+ /// }
+ /// assert_eq!(vec.len(), 10);
+ /// assert!(vec.capacity() >= 10);
+ ///
+ /// // ...but this may make the vector reallocate
+ /// vec.push(11);
+ /// assert_eq!(vec.len(), 11);
+ /// assert!(vec.capacity() >= 11);
+ ///
+ /// // A vector of a zero-sized type will always over-allocate, since no
+ /// // allocation is necessary
+ /// let vec_units = Vec::<()>::with_capacity(10);
+ /// assert_eq!(vec_units.capacity(), usize::MAX);
+ /// ```
+ #[cfg(not(no_global_oom_handling))]
+ #[inline]
+ #[stable(feature = "rust1", since = "1.0.0")]
+ #[must_use]
+ pub fn with_capacity(capacity: usize) -> Self {
+ Self::with_capacity_in(capacity, Global)
+ }
+
+ /// Tries to construct a new, empty `Vec<T>` with at least the specified capacity.
+ ///
+ /// The vector will be able to hold at least `capacity` elements without
+ /// reallocating. This method is allowed to allocate for more elements than
+ /// `capacity`. If `capacity` is 0, the vector will not allocate.
+ ///
+ /// It is important to note that although the returned vector has the
+ /// minimum *capacity* specified, the vector will have a zero *length*. For
+ /// an explanation of the difference between length and capacity, see
+ /// *[Capacity and reallocation]*.
+ ///
+ /// If it is important to know the exact allocated capacity of a `Vec`,
+ /// always use the [`capacity`] method after construction.
+ ///
+ /// For `Vec<T>` where `T` is a zero-sized type, there will be no allocation
+ /// and the capacity will always be `usize::MAX`.
+ ///
+ /// [Capacity and reallocation]: #capacity-and-reallocation
+ /// [`capacity`]: Vec::capacity
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = Vec::try_with_capacity(10).unwrap();
+ ///
+ /// // The vector contains no items, even though it has capacity for more
+ /// assert_eq!(vec.len(), 0);
+ /// assert!(vec.capacity() >= 10);
+ ///
+ /// // These are all done without reallocating...
+ /// for i in 0..10 {
+ /// vec.push(i);
+ /// }
+ /// assert_eq!(vec.len(), 10);
+ /// assert!(vec.capacity() >= 10);
+ ///
+ /// // ...but this may make the vector reallocate
+ /// vec.push(11);
+ /// assert_eq!(vec.len(), 11);
+ /// assert!(vec.capacity() >= 11);
+ ///
+ /// let mut result = Vec::try_with_capacity(usize::MAX);
+ /// assert!(result.is_err());
+ ///
+ /// // A vector of a zero-sized type will always over-allocate, since no
+ /// // allocation is necessary
+ /// let vec_units = Vec::<()>::try_with_capacity(10).unwrap();
+ /// assert_eq!(vec_units.capacity(), usize::MAX);
+ /// ```
+ #[inline]
+ #[stable(feature = "kernel", since = "1.0.0")]
+ pub fn try_with_capacity(capacity: usize) -> Result<Self, TryReserveError> {
+ Self::try_with_capacity_in(capacity, Global)
+ }
+
+ /// Creates a `Vec<T>` directly from a pointer, a capacity, and a length.
+ ///
+ /// # Safety
+ ///
+ /// This is highly unsafe, due to the number of invariants that aren't
+ /// checked:
+ ///
+ /// * `ptr` must have been allocated using the global allocator, such as via
+ /// the [`alloc::alloc`] function.
+ /// * `T` needs to have the same alignment as what `ptr` was allocated with.
+ /// (`T` having a less strict alignment is not sufficient, the alignment really
+ /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
+ /// allocated and deallocated with the same layout.)
+ /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
+ /// to be the same size as the pointer was allocated with. (Because similar to
+ /// alignment, [`dealloc`] must be called with the same layout `size`.)
+ /// * `length` needs to be less than or equal to `capacity`.
+ /// * The first `length` values must be properly initialized values of type `T`.
+ /// * `capacity` needs to be the capacity that the pointer was allocated with.
+ /// * The allocated size in bytes must be no larger than `isize::MAX`.
+ /// See the safety documentation of [`pointer::offset`].
+ ///
+ /// These requirements are always upheld by any `ptr` that has been allocated
+ /// via `Vec<T>`. Other allocation sources are allowed if the invariants are
+ /// upheld.
+ ///
+ /// Violating these may cause problems like corrupting the allocator's
+ /// internal data structures. For example it is normally **not** safe
+ /// to build a `Vec<u8>` from a pointer to a C `char` array with length
+ /// `size_t`, doing so is only safe if the array was initially allocated by
+ /// a `Vec` or `String`.
+ /// It's also not safe to build one from a `Vec<u16>` and its length, because
+ /// the allocator cares about the alignment, and these two types have different
+ /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
+ /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1. To avoid
+ /// these issues, it is often preferable to do casting/transmuting using
+ /// [`slice::from_raw_parts`] instead.
+ ///
+ /// The ownership of `ptr` is effectively transferred to the
+ /// `Vec<T>` which may then deallocate, reallocate or change the
+ /// contents of memory pointed to by the pointer at will. Ensure
+ /// that nothing else uses the pointer after calling this
+ /// function.
+ ///
+ /// [`String`]: crate::string::String
+ /// [`alloc::alloc`]: crate::alloc::alloc
+ /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::ptr;
+ /// use std::mem;
+ ///
+ /// let v = vec![1, 2, 3];
+ ///
+ // FIXME Update this when vec_into_raw_parts is stabilized
+ /// // Prevent running `v`'s destructor so we are in complete control
+ /// // of the allocation.
+ /// let mut v = mem::ManuallyDrop::new(v);
+ ///
+ /// // Pull out the various important pieces of information about `v`
+ /// let p = v.as_mut_ptr();
+ /// let len = v.len();
+ /// let cap = v.capacity();
+ ///
+ /// unsafe {
+ /// // Overwrite memory with 4, 5, 6
+ /// for i in 0..len {
+ /// ptr::write(p.add(i), 4 + i);
+ /// }
+ ///
+ /// // Put everything back together into a Vec
+ /// let rebuilt = Vec::from_raw_parts(p, len, cap);
+ /// assert_eq!(rebuilt, [4, 5, 6]);
+ /// }
+ /// ```
+ ///
+ /// Using memory that was allocated elsewhere:
+ ///
+ /// ```rust
+ /// #![feature(allocator_api)]
+ ///
+ /// use std::alloc::{AllocError, Allocator, Global, Layout};
+ ///
+ /// fn main() {
+ /// let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
+ ///
+ /// let vec = unsafe {
+ /// let mem = match Global.allocate(layout) {
+ /// Ok(mem) => mem.cast::<u32>().as_ptr(),
+ /// Err(AllocError) => return,
+ /// };
+ ///
+ /// mem.write(1_000_000);
+ ///
+ /// Vec::from_raw_parts_in(mem, 1, 16, Global)
+ /// };
+ ///
+ /// assert_eq!(vec, &[1_000_000]);
+ /// assert_eq!(vec.capacity(), 16);
+ /// }
+ /// ```
+ #[inline]
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Self {
+ unsafe { Self::from_raw_parts_in(ptr, length, capacity, Global) }
+ }
+}
+
+impl<T, A: Allocator> Vec<T, A> {
+ /// Constructs a new, empty `Vec<T, A>`.
+ ///
+ /// The vector will not allocate until elements are pushed onto it.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// #![feature(allocator_api)]
+ ///
+ /// use std::alloc::System;
+ ///
+ /// # #[allow(unused_mut)]
+ /// let mut vec: Vec<i32, _> = Vec::new_in(System);
+ /// ```
+ #[inline]
+ #[unstable(feature = "allocator_api", issue = "32838")]
+ pub const fn new_in(alloc: A) -> Self {
+ Vec { buf: RawVec::new_in(alloc), len: 0 }
+ }
+
+ /// Constructs a new, empty `Vec<T, A>` with at least the specified capacity
+ /// with the provided allocator.
+ ///
+ /// The vector will be able to hold at least `capacity` elements without
+ /// reallocating. This method is allowed to allocate for more elements than
+ /// `capacity`. If `capacity` is 0, the vector will not allocate.
+ ///
+ /// It is important to note that although the returned vector has the
+ /// minimum *capacity* specified, the vector will have a zero *length*. For
+ /// an explanation of the difference between length and capacity, see
+ /// *[Capacity and reallocation]*.
+ ///
+ /// If it is important to know the exact allocated capacity of a `Vec`,
+ /// always use the [`capacity`] method after construction.
+ ///
+ /// For `Vec<T, A>` where `T` is a zero-sized type, there will be no allocation
+ /// and the capacity will always be `usize::MAX`.
+ ///
+ /// [Capacity and reallocation]: #capacity-and-reallocation
+ /// [`capacity`]: Vec::capacity
+ ///
+ /// # Panics
+ ///
+ /// Panics if the new capacity exceeds `isize::MAX` bytes.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// #![feature(allocator_api)]
+ ///
+ /// use std::alloc::System;
+ ///
+ /// let mut vec = Vec::with_capacity_in(10, System);
+ ///
+ /// // The vector contains no items, even though it has capacity for more
+ /// assert_eq!(vec.len(), 0);
+ /// assert!(vec.capacity() >= 10);
+ ///
+ /// // These are all done without reallocating...
+ /// for i in 0..10 {
+ /// vec.push(i);
+ /// }
+ /// assert_eq!(vec.len(), 10);
+ /// assert!(vec.capacity() >= 10);
+ ///
+ /// // ...but this may make the vector reallocate
+ /// vec.push(11);
+ /// assert_eq!(vec.len(), 11);
+ /// assert!(vec.capacity() >= 11);
+ ///
+ /// // A vector of a zero-sized type will always over-allocate, since no
+ /// // allocation is necessary
+ /// let vec_units = Vec::<(), System>::with_capacity_in(10, System);
+ /// assert_eq!(vec_units.capacity(), usize::MAX);
+ /// ```
+ #[cfg(not(no_global_oom_handling))]
+ #[inline]
+ #[unstable(feature = "allocator_api", issue = "32838")]
+ pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
+ Vec { buf: RawVec::with_capacity_in(capacity, alloc), len: 0 }
+ }
+
+ /// Tries to construct a new, empty `Vec<T, A>` with at least the specified capacity
+ /// with the provided allocator.
+ ///
+ /// The vector will be able to hold at least `capacity` elements without
+ /// reallocating. This method is allowed to allocate for more elements than
+ /// `capacity`. If `capacity` is 0, the vector will not allocate.
+ ///
+ /// It is important to note that although the returned vector has the
+ /// minimum *capacity* specified, the vector will have a zero *length*. For
+ /// an explanation of the difference between length and capacity, see
+ /// *[Capacity and reallocation]*.
+ ///
+ /// If it is important to know the exact allocated capacity of a `Vec`,
+ /// always use the [`capacity`] method after construction.
+ ///
+ /// For `Vec<T, A>` where `T` is a zero-sized type, there will be no allocation
+ /// and the capacity will always be `usize::MAX`.
+ ///
+ /// [Capacity and reallocation]: #capacity-and-reallocation
+ /// [`capacity`]: Vec::capacity
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// #![feature(allocator_api)]
+ ///
+ /// use std::alloc::System;
+ ///
+ /// let mut vec = Vec::try_with_capacity_in(10, System).unwrap();
+ ///
+ /// // The vector contains no items, even though it has capacity for more
+ /// assert_eq!(vec.len(), 0);
+ /// assert!(vec.capacity() >= 10);
+ ///
+ /// // These are all done without reallocating...
+ /// for i in 0..10 {
+ /// vec.push(i);
+ /// }
+ /// assert_eq!(vec.len(), 10);
+ /// assert!(vec.capacity() >= 10);
+ ///
+ /// // ...but this may make the vector reallocate
+ /// vec.push(11);
+ /// assert_eq!(vec.len(), 11);
+ /// assert!(vec.capacity() >= 11);
+ ///
+ /// let mut result = Vec::try_with_capacity_in(usize::MAX, System);
+ /// assert!(result.is_err());
+ ///
+ /// // A vector of a zero-sized type will always over-allocate, since no
+ /// // allocation is necessary
+ /// let vec_units = Vec::<(), System>::try_with_capacity_in(10, System).unwrap();
+ /// assert_eq!(vec_units.capacity(), usize::MAX);
+ /// ```
+ #[inline]
+ #[stable(feature = "kernel", since = "1.0.0")]
+ pub fn try_with_capacity_in(capacity: usize, alloc: A) -> Result<Self, TryReserveError> {
+ Ok(Vec { buf: RawVec::try_with_capacity_in(capacity, alloc)?, len: 0 })
+ }
+
+ /// Creates a `Vec<T, A>` directly from a pointer, a capacity, a length,
+ /// and an allocator.
+ ///
+ /// # Safety
+ ///
+ /// This is highly unsafe, due to the number of invariants that aren't
+ /// checked:
+ ///
+ /// * `ptr` must be [*currently allocated*] via the given allocator `alloc`.
+ /// * `T` needs to have the same alignment as what `ptr` was allocated with.
+ /// (`T` having a less strict alignment is not sufficient, the alignment really
+ /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
+ /// allocated and deallocated with the same layout.)
+ /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
+ /// to be the same size as the pointer was allocated with. (Because similar to
+ /// alignment, [`dealloc`] must be called with the same layout `size`.)
+ /// * `length` needs to be less than or equal to `capacity`.
+ /// * The first `length` values must be properly initialized values of type `T`.
+ /// * `capacity` needs to [*fit*] the layout size that the pointer was allocated with.
+ /// * The allocated size in bytes must be no larger than `isize::MAX`.
+ /// See the safety documentation of [`pointer::offset`].
+ ///
+ /// These requirements are always upheld by any `ptr` that has been allocated
+ /// via `Vec<T, A>`. Other allocation sources are allowed if the invariants are
+ /// upheld.
+ ///
+ /// Violating these may cause problems like corrupting the allocator's
+ /// internal data structures. For example it is **not** safe
+ /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
+ /// It's also not safe to build one from a `Vec<u16>` and its length, because
+ /// the allocator cares about the alignment, and these two types have different
+ /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
+ /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
+ ///
+ /// The ownership of `ptr` is effectively transferred to the
+ /// `Vec<T>` which may then deallocate, reallocate or change the
+ /// contents of memory pointed to by the pointer at will. Ensure
+ /// that nothing else uses the pointer after calling this
+ /// function.
+ ///
+ /// [`String`]: crate::string::String
+ /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
+ /// [*currently allocated*]: crate::alloc::Allocator#currently-allocated-memory
+ /// [*fit*]: crate::alloc::Allocator#memory-fitting
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// #![feature(allocator_api)]
+ ///
+ /// use std::alloc::System;
+ ///
+ /// use std::ptr;
+ /// use std::mem;
+ ///
+ /// let mut v = Vec::with_capacity_in(3, System);
+ /// v.push(1);
+ /// v.push(2);
+ /// v.push(3);
+ ///
+ // FIXME Update this when vec_into_raw_parts is stabilized
+ /// // Prevent running `v`'s destructor so we are in complete control
+ /// // of the allocation.
+ /// let mut v = mem::ManuallyDrop::new(v);
+ ///
+ /// // Pull out the various important pieces of information about `v`
+ /// let p = v.as_mut_ptr();
+ /// let len = v.len();
+ /// let cap = v.capacity();
+ /// let alloc = v.allocator();
+ ///
+ /// unsafe {
+ /// // Overwrite memory with 4, 5, 6
+ /// for i in 0..len {
+ /// ptr::write(p.add(i), 4 + i);
+ /// }
+ ///
+ /// // Put everything back together into a Vec
+ /// let rebuilt = Vec::from_raw_parts_in(p, len, cap, alloc.clone());
+ /// assert_eq!(rebuilt, [4, 5, 6]);
+ /// }
+ /// ```
+ ///
+ /// Using memory that was allocated elsewhere:
+ ///
+ /// ```rust
+ /// use std::alloc::{alloc, Layout};
+ ///
+ /// fn main() {
+ /// let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
+ /// let vec = unsafe {
+ /// let mem = alloc(layout).cast::<u32>();
+ /// if mem.is_null() {
+ /// return;
+ /// }
+ ///
+ /// mem.write(1_000_000);
+ ///
+ /// Vec::from_raw_parts(mem, 1, 16)
+ /// };
+ ///
+ /// assert_eq!(vec, &[1_000_000]);
+ /// assert_eq!(vec.capacity(), 16);
+ /// }
+ /// ```
+ #[inline]
+ #[unstable(feature = "allocator_api", issue = "32838")]
+ pub unsafe fn from_raw_parts_in(ptr: *mut T, length: usize, capacity: usize, alloc: A) -> Self {
+ unsafe { Vec { buf: RawVec::from_raw_parts_in(ptr, capacity, alloc), len: length } }
+ }
+
+ /// Decomposes a `Vec<T>` into its raw components.
+ ///
+ /// Returns the raw pointer to the underlying data, the length of
+ /// the vector (in elements), and the allocated capacity of the
+ /// data (in elements). These are the same arguments in the same
+ /// order as the arguments to [`from_raw_parts`].
+ ///
+ /// After calling this function, the caller is responsible for the
+ /// memory previously managed by the `Vec`. The only way to do
+ /// this is to convert the raw pointer, length, and capacity back
+ /// into a `Vec` with the [`from_raw_parts`] function, allowing
+ /// the destructor to perform the cleanup.
+ ///
+ /// [`from_raw_parts`]: Vec::from_raw_parts
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// #![feature(vec_into_raw_parts)]
+ /// let v: Vec<i32> = vec![-1, 0, 1];
+ ///
+ /// let (ptr, len, cap) = v.into_raw_parts();
+ ///
+ /// let rebuilt = unsafe {
+ /// // We can now make changes to the components, such as
+ /// // transmuting the raw pointer to a compatible type.
+ /// let ptr = ptr as *mut u32;
+ ///
+ /// Vec::from_raw_parts(ptr, len, cap)
+ /// };
+ /// assert_eq!(rebuilt, [4294967295, 0, 1]);
+ /// ```
+ #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
+ pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
+ let mut me = ManuallyDrop::new(self);
+ (me.as_mut_ptr(), me.len(), me.capacity())
+ }
+
+ /// Decomposes a `Vec<T>` into its raw components.
+ ///
+ /// Returns the raw pointer to the underlying data, the length of the vector (in elements),
+ /// the allocated capacity of the data (in elements), and the allocator. These are the same
+ /// arguments in the same order as the arguments to [`from_raw_parts_in`].
+ ///
+ /// After calling this function, the caller is responsible for the
+ /// memory previously managed by the `Vec`. The only way to do
+ /// this is to convert the raw pointer, length, and capacity back
+ /// into a `Vec` with the [`from_raw_parts_in`] function, allowing
+ /// the destructor to perform the cleanup.
+ ///
+ /// [`from_raw_parts_in`]: Vec::from_raw_parts_in
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// #![feature(allocator_api, vec_into_raw_parts)]
+ ///
+ /// use std::alloc::System;
+ ///
+ /// let mut v: Vec<i32, System> = Vec::new_in(System);
+ /// v.push(-1);
+ /// v.push(0);
+ /// v.push(1);
+ ///
+ /// let (ptr, len, cap, alloc) = v.into_raw_parts_with_alloc();
+ ///
+ /// let rebuilt = unsafe {
+ /// // We can now make changes to the components, such as
+ /// // transmuting the raw pointer to a compatible type.
+ /// let ptr = ptr as *mut u32;
+ ///
+ /// Vec::from_raw_parts_in(ptr, len, cap, alloc)
+ /// };
+ /// assert_eq!(rebuilt, [4294967295, 0, 1]);
+ /// ```
+ #[unstable(feature = "allocator_api", issue = "32838")]
+ // #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
+ pub fn into_raw_parts_with_alloc(self) -> (*mut T, usize, usize, A) {
+ let mut me = ManuallyDrop::new(self);
+ let len = me.len();
+ let capacity = me.capacity();
+ let ptr = me.as_mut_ptr();
+ let alloc = unsafe { ptr::read(me.allocator()) };
+ (ptr, len, capacity, alloc)
+ }
+
+ /// Returns the total number of elements the vector can hold without
+ /// reallocating.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec: Vec<i32> = Vec::with_capacity(10);
+ /// vec.push(42);
+ /// assert!(vec.capacity() >= 10);
+ /// ```
+ #[inline]
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn capacity(&self) -> usize {
+ self.buf.capacity()
+ }
+
+ /// Reserves capacity for at least `additional` more elements to be inserted
+ /// in the given `Vec<T>`. The collection may reserve more space to
+ /// speculatively avoid frequent reallocations. After calling `reserve`,
+ /// capacity will be greater than or equal to `self.len() + additional`.
+ /// Does nothing if capacity is already sufficient.
+ ///
+ /// # Panics
+ ///
+ /// Panics if the new capacity exceeds `isize::MAX` bytes.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec![1];
+ /// vec.reserve(10);
+ /// assert!(vec.capacity() >= 11);
+ /// ```
+ #[cfg(not(no_global_oom_handling))]
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn reserve(&mut self, additional: usize) {
+ self.buf.reserve(self.len, additional);
+ }
+
+ /// Reserves the minimum capacity for at least `additional` more elements to
+ /// be inserted in the given `Vec<T>`. Unlike [`reserve`], this will not
+ /// deliberately over-allocate to speculatively avoid frequent allocations.
+ /// After calling `reserve_exact`, capacity will be greater than or equal to
+ /// `self.len() + additional`. Does nothing if the capacity is already
+ /// sufficient.
+ ///
+ /// Note that the allocator may give the collection more space than it
+ /// requests. Therefore, capacity can not be relied upon to be precisely
+ /// minimal. Prefer [`reserve`] if future insertions are expected.
+ ///
+ /// [`reserve`]: Vec::reserve
+ ///
+ /// # Panics
+ ///
+ /// Panics if the new capacity exceeds `isize::MAX` bytes.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec![1];
+ /// vec.reserve_exact(10);
+ /// assert!(vec.capacity() >= 11);
+ /// ```
+ #[cfg(not(no_global_oom_handling))]
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn reserve_exact(&mut self, additional: usize) {
+ self.buf.reserve_exact(self.len, additional);
+ }
+
+ /// Tries to reserve capacity for at least `additional` more elements to be inserted
+ /// in the given `Vec<T>`. The collection may reserve more space to speculatively avoid
+ /// frequent reallocations. After calling `try_reserve`, capacity will be
+ /// greater than or equal to `self.len() + additional` if it returns
+ /// `Ok(())`. Does nothing if capacity is already sufficient. This method
+ /// preserves the contents even if an error occurs.
+ ///
+ /// # Errors
+ ///
+ /// If the capacity overflows, or the allocator reports a failure, then an error
+ /// is returned.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::collections::TryReserveError;
+ ///
+ /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
+ /// let mut output = Vec::new();
+ ///
+ /// // Pre-reserve the memory, exiting if we can't
+ /// output.try_reserve(data.len())?;
+ ///
+ /// // Now we know this can't OOM in the middle of our complex work
+ /// output.extend(data.iter().map(|&val| {
+ /// val * 2 + 5 // very complicated
+ /// }));
+ ///
+ /// Ok(output)
+ /// }
+ /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
+ /// ```
+ #[stable(feature = "try_reserve", since = "1.57.0")]
+ pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
+ self.buf.try_reserve(self.len, additional)
+ }
+
+ /// Tries to reserve the minimum capacity for at least `additional`
+ /// elements to be inserted in the given `Vec<T>`. Unlike [`try_reserve`],
+ /// this will not deliberately over-allocate to speculatively avoid frequent
+ /// allocations. After calling `try_reserve_exact`, capacity will be greater
+ /// than or equal to `self.len() + additional` if it returns `Ok(())`.
+ /// Does nothing if the capacity is already sufficient.
+ ///
+ /// Note that the allocator may give the collection more space than it
+ /// requests. Therefore, capacity can not be relied upon to be precisely
+ /// minimal. Prefer [`try_reserve`] if future insertions are expected.
+ ///
+ /// [`try_reserve`]: Vec::try_reserve
+ ///
+ /// # Errors
+ ///
+ /// If the capacity overflows, or the allocator reports a failure, then an error
+ /// is returned.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::collections::TryReserveError;
+ ///
+ /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
+ /// let mut output = Vec::new();
+ ///
+ /// // Pre-reserve the memory, exiting if we can't
+ /// output.try_reserve_exact(data.len())?;
+ ///
+ /// // Now we know this can't OOM in the middle of our complex work
+ /// output.extend(data.iter().map(|&val| {
+ /// val * 2 + 5 // very complicated
+ /// }));
+ ///
+ /// Ok(output)
+ /// }
+ /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
+ /// ```
+ #[stable(feature = "try_reserve", since = "1.57.0")]
+ pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
+ self.buf.try_reserve_exact(self.len, additional)
+ }
+
+ /// Shrinks the capacity of the vector as much as possible.
+ ///
+ /// It will drop down as close as possible to the length but the allocator
+ /// may still inform the vector that there is space for a few more elements.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = Vec::with_capacity(10);
+ /// vec.extend([1, 2, 3]);
+ /// assert!(vec.capacity() >= 10);
+ /// vec.shrink_to_fit();
+ /// assert!(vec.capacity() >= 3);
+ /// ```
+ #[cfg(not(no_global_oom_handling))]
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn shrink_to_fit(&mut self) {
+ // The capacity is never less than the length, and there's nothing to do when
+ // they are equal, so we can avoid the panic case in `RawVec::shrink_to_fit`
+ // by only calling it with a greater capacity.
+ if self.capacity() > self.len {
+ self.buf.shrink_to_fit(self.len);
+ }
+ }
+
+ /// Shrinks the capacity of the vector with a lower bound.
+ ///
+ /// The capacity will remain at least as large as both the length
+ /// and the supplied value.
+ ///
+ /// If the current capacity is less than the lower limit, this is a no-op.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = Vec::with_capacity(10);
+ /// vec.extend([1, 2, 3]);
+ /// assert!(vec.capacity() >= 10);
+ /// vec.shrink_to(4);
+ /// assert!(vec.capacity() >= 4);
+ /// vec.shrink_to(0);
+ /// assert!(vec.capacity() >= 3);
+ /// ```
+ #[cfg(not(no_global_oom_handling))]
+ #[stable(feature = "shrink_to", since = "1.56.0")]
+ pub fn shrink_to(&mut self, min_capacity: usize) {
+ if self.capacity() > min_capacity {
+ self.buf.shrink_to_fit(cmp::max(self.len, min_capacity));
+ }
+ }
+
+ /// Converts the vector into [`Box<[T]>`][owned slice].
+ ///
+ /// If the vector has excess capacity, its items will be moved into a
+ /// newly-allocated buffer with exactly the right capacity.
+ ///
+ /// [owned slice]: Box
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let v = vec![1, 2, 3];
+ ///
+ /// let slice = v.into_boxed_slice();
+ /// ```
+ ///
+ /// Any excess capacity is removed:
+ ///
+ /// ```
+ /// let mut vec = Vec::with_capacity(10);
+ /// vec.extend([1, 2, 3]);
+ ///
+ /// assert!(vec.capacity() >= 10);
+ /// let slice = vec.into_boxed_slice();
+ /// assert_eq!(slice.into_vec().capacity(), 3);
+ /// ```
+ #[cfg(not(no_global_oom_handling))]
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn into_boxed_slice(mut self) -> Box<[T], A> {
+ unsafe {
+ self.shrink_to_fit();
+ let me = ManuallyDrop::new(self);
+ let buf = ptr::read(&me.buf);
+ let len = me.len();
+ buf.into_box(len).assume_init()
+ }
+ }
+
+ /// Shortens the vector, keeping the first `len` elements and dropping
+ /// the rest.
+ ///
+ /// If `len` is greater than the vector's current length, this has no
+ /// effect.
+ ///
+ /// The [`drain`] method can emulate `truncate`, but causes the excess
+ /// elements to be returned instead of dropped.
+ ///
+ /// Note that this method has no effect on the allocated capacity
+ /// of the vector.
+ ///
+ /// # Examples
+ ///
+ /// Truncating a five element vector to two elements:
+ ///
+ /// ```
+ /// let mut vec = vec![1, 2, 3, 4, 5];
+ /// vec.truncate(2);
+ /// assert_eq!(vec, [1, 2]);
+ /// ```
+ ///
+ /// No truncation occurs when `len` is greater than the vector's current
+ /// length:
+ ///
+ /// ```
+ /// let mut vec = vec![1, 2, 3];
+ /// vec.truncate(8);
+ /// assert_eq!(vec, [1, 2, 3]);
+ /// ```
+ ///
+ /// Truncating when `len == 0` is equivalent to calling the [`clear`]
+ /// method.
+ ///
+ /// ```
+ /// let mut vec = vec![1, 2, 3];
+ /// vec.truncate(0);
+ /// assert_eq!(vec, []);
+ /// ```
+ ///
+ /// [`clear`]: Vec::clear
+ /// [`drain`]: Vec::drain
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn truncate(&mut self, len: usize) {
+ // This is safe because:
+ //
+ // * the slice passed to `drop_in_place` is valid; the `len > self.len`
+ // case avoids creating an invalid slice, and
+ // * the `len` of the vector is shrunk before calling `drop_in_place`,
+ // such that no value will be dropped twice in case `drop_in_place`
+ // were to panic once (if it panics twice, the program aborts).
+ unsafe {
+ // Note: It's intentional that this is `>` and not `>=`.
+ // Changing it to `>=` has negative performance
+ // implications in some cases. See #78884 for more.
+ if len > self.len {
+ return;
+ }
+ let remaining_len = self.len - len;
+ let s = ptr::slice_from_raw_parts_mut(self.as_mut_ptr().add(len), remaining_len);
+ self.len = len;
+ ptr::drop_in_place(s);
+ }
+ }
+
+ /// Extracts a slice containing the entire vector.
+ ///
+ /// Equivalent to `&s[..]`.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::io::{self, Write};
+ /// let buffer = vec![1, 2, 3, 5, 8];
+ /// io::sink().write(buffer.as_slice()).unwrap();
+ /// ```
+ #[inline]
+ #[stable(feature = "vec_as_slice", since = "1.7.0")]
+ pub fn as_slice(&self) -> &[T] {
+ self
+ }
+
+ /// Extracts a mutable slice of the entire vector.
+ ///
+ /// Equivalent to `&mut s[..]`.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::io::{self, Read};
+ /// let mut buffer = vec![0; 3];
+ /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
+ /// ```
+ #[inline]
+ #[stable(feature = "vec_as_slice", since = "1.7.0")]
+ pub fn as_mut_slice(&mut self) -> &mut [T] {
+ self
+ }
+
+ /// Returns a raw pointer to the vector's buffer, or a dangling raw pointer
+ /// valid for zero sized reads if the vector didn't allocate.
+ ///
+ /// The caller must ensure that the vector outlives the pointer this
+ /// function returns, or else it will end up pointing to garbage.
+ /// Modifying the vector may cause its buffer to be reallocated,
+ /// which would also make any pointers to it invalid.
+ ///
+ /// The caller must also ensure that the memory the pointer (non-transitively) points to
+ /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
+ /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let x = vec![1, 2, 4];
+ /// let x_ptr = x.as_ptr();
+ ///
+ /// unsafe {
+ /// for i in 0..x.len() {
+ /// assert_eq!(*x_ptr.add(i), 1 << i);
+ /// }
+ /// }
+ /// ```
+ ///
+ /// [`as_mut_ptr`]: Vec::as_mut_ptr
+ #[stable(feature = "vec_as_ptr", since = "1.37.0")]
+ #[inline]
+ pub fn as_ptr(&self) -> *const T {
+ // We shadow the slice method of the same name to avoid going through
+ // `deref`, which creates an intermediate reference.
+ self.buf.ptr()
+ }
+
+ /// Returns an unsafe mutable pointer to the vector's buffer, or a dangling
+ /// raw pointer valid for zero sized reads if the vector didn't allocate.
+ ///
+ /// The caller must ensure that the vector outlives the pointer this
+ /// function returns, or else it will end up pointing to garbage.
+ /// Modifying the vector may cause its buffer to be reallocated,
+ /// which would also make any pointers to it invalid.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// // Allocate vector big enough for 4 elements.
+ /// let size = 4;
+ /// let mut x: Vec<i32> = Vec::with_capacity(size);
+ /// let x_ptr = x.as_mut_ptr();
+ ///
+ /// // Initialize elements via raw pointer writes, then set length.
+ /// unsafe {
+ /// for i in 0..size {
+ /// *x_ptr.add(i) = i as i32;
+ /// }
+ /// x.set_len(size);
+ /// }
+ /// assert_eq!(&*x, &[0, 1, 2, 3]);
+ /// ```
+ #[stable(feature = "vec_as_ptr", since = "1.37.0")]
+ #[inline]
+ pub fn as_mut_ptr(&mut self) -> *mut T {
+ // We shadow the slice method of the same name to avoid going through
+ // `deref_mut`, which creates an intermediate reference.
+ self.buf.ptr()
+ }
+
+ /// Returns a reference to the underlying allocator.
+ #[unstable(feature = "allocator_api", issue = "32838")]
+ #[inline]
+ pub fn allocator(&self) -> &A {
+ self.buf.allocator()
+ }
+
+ /// Forces the length of the vector to `new_len`.
+ ///
+ /// This is a low-level operation that maintains none of the normal
+ /// invariants of the type. Normally changing the length of a vector
+ /// is done using one of the safe operations instead, such as
+ /// [`truncate`], [`resize`], [`extend`], or [`clear`].
+ ///
+ /// [`truncate`]: Vec::truncate
+ /// [`resize`]: Vec::resize
+ /// [`extend`]: Extend::extend
+ /// [`clear`]: Vec::clear
+ ///
+ /// # Safety
+ ///
+ /// - `new_len` must be less than or equal to [`capacity()`].
+ /// - The elements at `old_len..new_len` must be initialized.
+ ///
+ /// [`capacity()`]: Vec::capacity
+ ///
+ /// # Examples
+ ///
+ /// This method can be useful for situations in which the vector
+ /// is serving as a buffer for other code, particularly over FFI:
+ ///
+ /// ```no_run
+ /// # #![allow(dead_code)]
+ /// # // This is just a minimal skeleton for the doc example;
+ /// # // don't use this as a starting point for a real library.
+ /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
+ /// # const Z_OK: i32 = 0;
+ /// # extern "C" {
+ /// # fn deflateGetDictionary(
+ /// # strm: *mut std::ffi::c_void,
+ /// # dictionary: *mut u8,
+ /// # dictLength: *mut usize,
+ /// # ) -> i32;
+ /// # }
+ /// # impl StreamWrapper {
+ /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
+ /// // Per the FFI method's docs, "32768 bytes is always enough".
+ /// let mut dict = Vec::with_capacity(32_768);
+ /// let mut dict_length = 0;
+ /// // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
+ /// // 1. `dict_length` elements were initialized.
+ /// // 2. `dict_length` <= the capacity (32_768)
+ /// // which makes `set_len` safe to call.
+ /// unsafe {
+ /// // Make the FFI call...
+ /// let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
+ /// if r == Z_OK {
+ /// // ...and update the length to what was initialized.
+ /// dict.set_len(dict_length);
+ /// Some(dict)
+ /// } else {
+ /// None
+ /// }
+ /// }
+ /// }
+ /// # }
+ /// ```
+ ///
+ /// While the following example is sound, there is a memory leak since
+ /// the inner vectors were not freed prior to the `set_len` call:
+ ///
+ /// ```
+ /// let mut vec = vec![vec![1, 0, 0],
+ /// vec![0, 1, 0],
+ /// vec![0, 0, 1]];
+ /// // SAFETY:
+ /// // 1. `old_len..0` is empty so no elements need to be initialized.
+ /// // 2. `0 <= capacity` always holds whatever `capacity` is.
+ /// unsafe {
+ /// vec.set_len(0);
+ /// }
+ /// ```
+ ///
+ /// Normally, here, one would use [`clear`] instead to correctly drop
+ /// the contents and thus not leak memory.
+ #[inline]
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub unsafe fn set_len(&mut self, new_len: usize) {
+ debug_assert!(new_len <= self.capacity());
+
+ self.len = new_len;
+ }
+
+ /// Removes an element from the vector and returns it.
+ ///
+ /// The removed element is replaced by the last element of the vector.
+ ///
+ /// This does not preserve ordering, but is *O*(1).
+ /// If you need to preserve the element order, use [`remove`] instead.
+ ///
+ /// [`remove`]: Vec::remove
+ ///
+ /// # Panics
+ ///
+ /// Panics if `index` is out of bounds.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut v = vec!["foo", "bar", "baz", "qux"];
+ ///
+ /// assert_eq!(v.swap_remove(1), "bar");
+ /// assert_eq!(v, ["foo", "qux", "baz"]);
+ ///
+ /// assert_eq!(v.swap_remove(0), "foo");
+ /// assert_eq!(v, ["baz", "qux"]);
+ /// ```
+ #[inline]
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn swap_remove(&mut self, index: usize) -> T {
+ #[cold]
+ #[inline(never)]
+ fn assert_failed(index: usize, len: usize) -> ! {
+ panic!("swap_remove index (is {index}) should be < len (is {len})");
+ }
+
+ let len = self.len();
+ if index >= len {
+ assert_failed(index, len);
+ }
+ unsafe {
+ // We replace self[index] with the last element. Note that if the
+ // bounds check above succeeds there must be a last element (which
+ // can be self[index] itself).
+ let value = ptr::read(self.as_ptr().add(index));
+ let base_ptr = self.as_mut_ptr();
+ ptr::copy(base_ptr.add(len - 1), base_ptr.add(index), 1);
+ self.set_len(len - 1);
+ value
+ }
+ }
+
+ /// Inserts an element at position `index` within the vector, shifting all
+ /// elements after it to the right.
+ ///
+ /// # Panics
+ ///
+ /// Panics if `index > len`.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec![1, 2, 3];
+ /// vec.insert(1, 4);
+ /// assert_eq!(vec, [1, 4, 2, 3]);
+ /// vec.insert(4, 5);
+ /// assert_eq!(vec, [1, 4, 2, 3, 5]);
+ /// ```
+ #[cfg(not(no_global_oom_handling))]
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn insert(&mut self, index: usize, element: T) {
+ #[cold]
+ #[inline(never)]
+ fn assert_failed(index: usize, len: usize) -> ! {
+ panic!("insertion index (is {index}) should be <= len (is {len})");
+ }
+
+ let len = self.len();
+
+ // space for the new element
+ if len == self.buf.capacity() {
+ self.reserve(1);
+ }
+
+ unsafe {
+ // infallible
+ // The spot to put the new value
+ {
+ let p = self.as_mut_ptr().add(index);
+ if index < len {
+ // Shift everything over to make space. (Duplicating the
+ // `index`th element into two consecutive places.)
+ ptr::copy(p, p.add(1), len - index);
+ } else if index == len {
+ // No elements need shifting.
+ } else {
+ assert_failed(index, len);
+ }
+ // Write it in, overwriting the first copy of the `index`th
+ // element.
+ ptr::write(p, element);
+ }
+ self.set_len(len + 1);
+ }
+ }
+
+ /// Removes and returns the element at position `index` within the vector,
+ /// shifting all elements after it to the left.
+ ///
+ /// Note: Because this shifts over the remaining elements, it has a
+ /// worst-case performance of *O*(*n*). If you don't need the order of elements
+ /// to be preserved, use [`swap_remove`] instead. If you'd like to remove
+ /// elements from the beginning of the `Vec`, consider using
+ /// [`VecDeque::pop_front`] instead.
+ ///
+ /// [`swap_remove`]: Vec::swap_remove
+ /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
+ ///
+ /// # Panics
+ ///
+ /// Panics if `index` is out of bounds.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut v = vec![1, 2, 3];
+ /// assert_eq!(v.remove(1), 2);
+ /// assert_eq!(v, [1, 3]);
+ /// ```
+ #[stable(feature = "rust1", since = "1.0.0")]
+ #[track_caller]
+ pub fn remove(&mut self, index: usize) -> T {
+ #[cold]
+ #[inline(never)]
+ #[track_caller]
+ fn assert_failed(index: usize, len: usize) -> ! {
+ panic!("removal index (is {index}) should be < len (is {len})");
+ }
+
+ let len = self.len();
+ if index >= len {
+ assert_failed(index, len);
+ }
+ unsafe {
+ // infallible
+ let ret;
+ {
+ // the place we are taking from.
+ let ptr = self.as_mut_ptr().add(index);
+ // copy it out, unsafely having a copy of the value on
+ // the stack and in the vector at the same time.
+ ret = ptr::read(ptr);
+
+ // Shift everything down to fill in that spot.
+ ptr::copy(ptr.add(1), ptr, len - index - 1);
+ }
+ self.set_len(len - 1);
+ ret
+ }
+ }
+
+ /// Retains only the elements specified by the predicate.
+ ///
+ /// In other words, remove all elements `e` for which `f(&e)` returns `false`.
+ /// This method operates in place, visiting each element exactly once in the
+ /// original order, and preserves the order of the retained elements.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec![1, 2, 3, 4];
+ /// vec.retain(|&x| x % 2 == 0);
+ /// assert_eq!(vec, [2, 4]);
+ /// ```
+ ///
+ /// Because the elements are visited exactly once in the original order,
+ /// external state may be used to decide which elements to keep.
+ ///
+ /// ```
+ /// let mut vec = vec![1, 2, 3, 4, 5];
+ /// let keep = [false, true, true, false, true];
+ /// let mut iter = keep.iter();
+ /// vec.retain(|_| *iter.next().unwrap());
+ /// assert_eq!(vec, [2, 3, 5]);
+ /// ```
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn retain<F>(&mut self, mut f: F)
+ where
+ F: FnMut(&T) -> bool,
+ {
+ self.retain_mut(|elem| f(elem));
+ }
+
+ /// Retains only the elements specified by the predicate, passing a mutable reference to it.
+ ///
+ /// In other words, remove all elements `e` such that `f(&mut e)` returns `false`.
+ /// This method operates in place, visiting each element exactly once in the
+ /// original order, and preserves the order of the retained elements.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec![1, 2, 3, 4];
+ /// vec.retain_mut(|x| if *x <= 3 {
+ /// *x += 1;
+ /// true
+ /// } else {
+ /// false
+ /// });
+ /// assert_eq!(vec, [2, 3, 4]);
+ /// ```
+ #[stable(feature = "vec_retain_mut", since = "1.61.0")]
+ pub fn retain_mut<F>(&mut self, mut f: F)
+ where
+ F: FnMut(&mut T) -> bool,
+ {
+ let original_len = self.len();
+ // Avoid double drop if the drop guard is not executed,
+ // since we may make some holes during the process.
+ unsafe { self.set_len(0) };
+
+ // Vec: [Kept, Kept, Hole, Hole, Hole, Hole, Unchecked, Unchecked]
+ // |<- processed len ->| ^- next to check
+ // |<- deleted cnt ->|
+ // |<- original_len ->|
+ // Kept: Elements which predicate returns true on.
+ // Hole: Moved or dropped element slot.
+ // Unchecked: Unchecked valid elements.
+ //
+ // This drop guard will be invoked when predicate or `drop` of element panicked.
+ // It shifts unchecked elements to cover holes and `set_len` to the correct length.
+ // In cases when predicate and `drop` never panick, it will be optimized out.
+ struct BackshiftOnDrop<'a, T, A: Allocator> {
+ v: &'a mut Vec<T, A>,
+ processed_len: usize,
+ deleted_cnt: usize,
+ original_len: usize,
+ }
+
+ impl<T, A: Allocator> Drop for BackshiftOnDrop<'_, T, A> {
+ fn drop(&mut self) {
+ if self.deleted_cnt > 0 {
+ // SAFETY: Trailing unchecked items must be valid since we never touch them.
+ unsafe {
+ ptr::copy(
+ self.v.as_ptr().add(self.processed_len),
+ self.v.as_mut_ptr().add(self.processed_len - self.deleted_cnt),
+ self.original_len - self.processed_len,
+ );
+ }
+ }
+ // SAFETY: After filling holes, all items are in contiguous memory.
+ unsafe {
+ self.v.set_len(self.original_len - self.deleted_cnt);
+ }
+ }
+ }
+
+ let mut g = BackshiftOnDrop { v: self, processed_len: 0, deleted_cnt: 0, original_len };
+
+ fn process_loop<F, T, A: Allocator, const DELETED: bool>(
+ original_len: usize,
+ f: &mut F,
+ g: &mut BackshiftOnDrop<'_, T, A>,
+ ) where
+ F: FnMut(&mut T) -> bool,
+ {
+ while g.processed_len != original_len {
+ // SAFETY: Unchecked element must be valid.
+ let cur = unsafe { &mut *g.v.as_mut_ptr().add(g.processed_len) };
+ if !f(cur) {
+ // Advance early to avoid double drop if `drop_in_place` panicked.
+ g.processed_len += 1;
+ g.deleted_cnt += 1;
+ // SAFETY: We never touch this element again after dropped.
+ unsafe { ptr::drop_in_place(cur) };
+ // We already advanced the counter.
+ if DELETED {
+ continue;
+ } else {
+ break;
+ }
+ }
+ if DELETED {
+ // SAFETY: `deleted_cnt` > 0, so the hole slot must not overlap with current element.
+ // We use copy for move, and never touch this element again.
+ unsafe {
+ let hole_slot = g.v.as_mut_ptr().add(g.processed_len - g.deleted_cnt);
+ ptr::copy_nonoverlapping(cur, hole_slot, 1);
+ }
+ }
+ g.processed_len += 1;
+ }
+ }
+
+ // Stage 1: Nothing was deleted.
+ process_loop::<F, T, A, false>(original_len, &mut f, &mut g);
+
+ // Stage 2: Some elements were deleted.
+ process_loop::<F, T, A, true>(original_len, &mut f, &mut g);
+
+ // All item are processed. This can be optimized to `set_len` by LLVM.
+ drop(g);
+ }
+
+ /// Removes all but the first of consecutive elements in the vector that resolve to the same
+ /// key.
+ ///
+ /// If the vector is sorted, this removes all duplicates.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec![10, 20, 21, 30, 20];
+ ///
+ /// vec.dedup_by_key(|i| *i / 10);
+ ///
+ /// assert_eq!(vec, [10, 20, 30, 20]);
+ /// ```
+ #[stable(feature = "dedup_by", since = "1.16.0")]
+ #[inline]
+ pub fn dedup_by_key<F, K>(&mut self, mut key: F)
+ where
+ F: FnMut(&mut T) -> K,
+ K: PartialEq,
+ {
+ self.dedup_by(|a, b| key(a) == key(b))
+ }
+
+ /// Removes all but the first of consecutive elements in the vector satisfying a given equality
+ /// relation.
+ ///
+ /// The `same_bucket` function is passed references to two elements from the vector and
+ /// must determine if the elements compare equal. The elements are passed in opposite order
+ /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
+ ///
+ /// If the vector is sorted, this removes all duplicates.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
+ ///
+ /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
+ ///
+ /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
+ /// ```
+ #[stable(feature = "dedup_by", since = "1.16.0")]
+ pub fn dedup_by<F>(&mut self, mut same_bucket: F)
+ where
+ F: FnMut(&mut T, &mut T) -> bool,
+ {
+ let len = self.len();
+ if len <= 1 {
+ return;
+ }
+
+ /* INVARIANT: vec.len() > read >= write > write-1 >= 0 */
+ struct FillGapOnDrop<'a, T, A: core::alloc::Allocator> {
+ /* Offset of the element we want to check if it is duplicate */
+ read: usize,
+
+ /* Offset of the place where we want to place the non-duplicate
+ * when we find it. */
+ write: usize,
+
+ /* The Vec that would need correction if `same_bucket` panicked */
+ vec: &'a mut Vec<T, A>,
+ }
+
+ impl<'a, T, A: core::alloc::Allocator> Drop for FillGapOnDrop<'a, T, A> {
+ fn drop(&mut self) {
+ /* This code gets executed when `same_bucket` panics */
+
+ /* SAFETY: invariant guarantees that `read - write`
+ * and `len - read` never overflow and that the copy is always
+ * in-bounds. */
+ unsafe {
+ let ptr = self.vec.as_mut_ptr();
+ let len = self.vec.len();
+
+ /* How many items were left when `same_bucket` panicked.
+ * Basically vec[read..].len() */
+ let items_left = len.wrapping_sub(self.read);
+
+ /* Pointer to first item in vec[write..write+items_left] slice */
+ let dropped_ptr = ptr.add(self.write);
+ /* Pointer to first item in vec[read..] slice */
+ let valid_ptr = ptr.add(self.read);
+
+ /* Copy `vec[read..]` to `vec[write..write+items_left]`.
+ * The slices can overlap, so `copy_nonoverlapping` cannot be used */
+ ptr::copy(valid_ptr, dropped_ptr, items_left);
+
+ /* How many items have been already dropped
+ * Basically vec[read..write].len() */
+ let dropped = self.read.wrapping_sub(self.write);
+
+ self.vec.set_len(len - dropped);
+ }
+ }
+ }
+
+ let mut gap = FillGapOnDrop { read: 1, write: 1, vec: self };
+ let ptr = gap.vec.as_mut_ptr();
+
+ /* Drop items while going through Vec, it should be more efficient than
+ * doing slice partition_dedup + truncate */
+
+ /* SAFETY: Because of the invariant, read_ptr, prev_ptr and write_ptr
+ * are always in-bounds and read_ptr never aliases prev_ptr */
+ unsafe {
+ while gap.read < len {
+ let read_ptr = ptr.add(gap.read);
+ let prev_ptr = ptr.add(gap.write.wrapping_sub(1));
+
+ if same_bucket(&mut *read_ptr, &mut *prev_ptr) {
+ // Increase `gap.read` now since the drop may panic.
+ gap.read += 1;
+ /* We have found duplicate, drop it in-place */
+ ptr::drop_in_place(read_ptr);
+ } else {
+ let write_ptr = ptr.add(gap.write);
+
+ /* Because `read_ptr` can be equal to `write_ptr`, we either
+ * have to use `copy` or conditional `copy_nonoverlapping`.
+ * Looks like the first option is faster. */
+ ptr::copy(read_ptr, write_ptr, 1);
+
+ /* We have filled that place, so go further */
+ gap.write += 1;
+ gap.read += 1;
+ }
+ }
+
+ /* Technically we could let `gap` clean up with its Drop, but
+ * when `same_bucket` is guaranteed to not panic, this bloats a little
+ * the codegen, so we just do it manually */
+ gap.vec.set_len(gap.write);
+ mem::forget(gap);
+ }
+ }
+
+ /// Appends an element to the back of a collection.
+ ///
+ /// # Panics
+ ///
+ /// Panics if the new capacity exceeds `isize::MAX` bytes.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec![1, 2];
+ /// vec.push(3);
+ /// assert_eq!(vec, [1, 2, 3]);
+ /// ```
+ #[cfg(not(no_global_oom_handling))]
+ #[inline]
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn push(&mut self, value: T) {
+ // This will panic or abort if we would allocate > isize::MAX bytes
+ // or if the length increment would overflow for zero-sized types.
+ if self.len == self.buf.capacity() {
+ self.buf.reserve_for_push(self.len);
+ }
+ unsafe {
+ let end = self.as_mut_ptr().add(self.len);
+ ptr::write(end, value);
+ self.len += 1;
+ }
+ }
+
+ /// Tries to append an element to the back of a collection.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec![1, 2];
+ /// vec.try_push(3).unwrap();
+ /// assert_eq!(vec, [1, 2, 3]);
+ /// ```
+ #[inline]
+ #[stable(feature = "kernel", since = "1.0.0")]
+ pub fn try_push(&mut self, value: T) -> Result<(), TryReserveError> {
+ if self.len == self.buf.capacity() {
+ self.buf.try_reserve_for_push(self.len)?;
+ }
+ unsafe {
+ let end = self.as_mut_ptr().add(self.len);
+ ptr::write(end, value);
+ self.len += 1;
+ }
+ Ok(())
+ }
+
+ /// Appends an element if there is sufficient spare capacity, otherwise an error is returned
+ /// with the element.
+ ///
+ /// Unlike [`push`] this method will not reallocate when there's insufficient capacity.
+ /// The caller should use [`reserve`] or [`try_reserve`] to ensure that there is enough capacity.
+ ///
+ /// [`push`]: Vec::push
+ /// [`reserve`]: Vec::reserve
+ /// [`try_reserve`]: Vec::try_reserve
+ ///
+ /// # Examples
+ ///
+ /// A manual, panic-free alternative to [`FromIterator`]:
+ ///
+ /// ```
+ /// #![feature(vec_push_within_capacity)]
+ ///
+ /// use std::collections::TryReserveError;
+ /// fn from_iter_fallible<T>(iter: impl Iterator<Item=T>) -> Result<Vec<T>, TryReserveError> {
+ /// let mut vec = Vec::new();
+ /// for value in iter {
+ /// if let Err(value) = vec.push_within_capacity(value) {
+ /// vec.try_reserve(1)?;
+ /// // this cannot fail, the previous line either returned or added at least 1 free slot
+ /// let _ = vec.push_within_capacity(value);
+ /// }
+ /// }
+ /// Ok(vec)
+ /// }
+ /// assert_eq!(from_iter_fallible(0..100), Ok(Vec::from_iter(0..100)));
+ /// ```
+ #[inline]
+ #[unstable(feature = "vec_push_within_capacity", issue = "100486")]
+ pub fn push_within_capacity(&mut self, value: T) -> Result<(), T> {
+ if self.len == self.buf.capacity() {
+ return Err(value);
+ }
+ unsafe {
+ let end = self.as_mut_ptr().add(self.len);
+ ptr::write(end, value);
+ self.len += 1;
+ }
+ Ok(())
+ }
+
+ /// Removes the last element from a vector and returns it, or [`None`] if it
+ /// is empty.
+ ///
+ /// If you'd like to pop the first element, consider using
+ /// [`VecDeque::pop_front`] instead.
+ ///
+ /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec![1, 2, 3];
+ /// assert_eq!(vec.pop(), Some(3));
+ /// assert_eq!(vec, [1, 2]);
+ /// ```
+ #[inline]
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn pop(&mut self) -> Option<T> {
+ if self.len == 0 {
+ None
+ } else {
+ unsafe {
+ self.len -= 1;
+ Some(ptr::read(self.as_ptr().add(self.len())))
+ }
+ }
+ }
+
+ /// Moves all the elements of `other` into `self`, leaving `other` empty.
+ ///
+ /// # Panics
+ ///
+ /// Panics if the new capacity exceeds `isize::MAX` bytes.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec![1, 2, 3];
+ /// let mut vec2 = vec![4, 5, 6];
+ /// vec.append(&mut vec2);
+ /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
+ /// assert_eq!(vec2, []);
+ /// ```
+ #[cfg(not(no_global_oom_handling))]
+ #[inline]
+ #[stable(feature = "append", since = "1.4.0")]
+ pub fn append(&mut self, other: &mut Self) {
+ unsafe {
+ self.append_elements(other.as_slice() as _);
+ other.set_len(0);
+ }
+ }
+
+ /// Appends elements to `self` from other buffer.
+ #[cfg(not(no_global_oom_handling))]
+ #[inline]
+ unsafe fn append_elements(&mut self, other: *const [T]) {
+ let count = unsafe { (*other).len() };
+ self.reserve(count);
+ let len = self.len();
+ unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) };
+ self.len += count;
+ }
+
+ /// Tries to append elements to `self` from other buffer.
+ #[inline]
+ unsafe fn try_append_elements(&mut self, other: *const [T]) -> Result<(), TryReserveError> {
+ let count = unsafe { (*other).len() };
+ self.try_reserve(count)?;
+ let len = self.len();
+ unsafe { ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count) };
+ self.len += count;
+ Ok(())
+ }
+
+ /// Removes the specified range from the vector in bulk, returning all
+ /// removed elements as an iterator. If the iterator is dropped before
+ /// being fully consumed, it drops the remaining removed elements.
+ ///
+ /// The returned iterator keeps a mutable borrow on the vector to optimize
+ /// its implementation.
+ ///
+ /// # Panics
+ ///
+ /// Panics if the starting point is greater than the end point or if
+ /// the end point is greater than the length of the vector.
+ ///
+ /// # Leaking
+ ///
+ /// If the returned iterator goes out of scope without being dropped (due to
+ /// [`mem::forget`], for example), the vector may have lost and leaked
+ /// elements arbitrarily, including elements outside the range.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut v = vec![1, 2, 3];
+ /// let u: Vec<_> = v.drain(1..).collect();
+ /// assert_eq!(v, &[1]);
+ /// assert_eq!(u, &[2, 3]);
+ ///
+ /// // A full range clears the vector, like `clear()` does
+ /// v.drain(..);
+ /// assert_eq!(v, &[]);
+ /// ```
+ #[stable(feature = "drain", since = "1.6.0")]
+ pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A>
+ where
+ R: RangeBounds<usize>,
+ {
+ // Memory safety
+ //
+ // When the Drain is first created, it shortens the length of
+ // the source vector to make sure no uninitialized or moved-from elements
+ // are accessible at all if the Drain's destructor never gets to run.
+ //
+ // Drain will ptr::read out the values to remove.
+ // When finished, remaining tail of the vec is copied back to cover
+ // the hole, and the vector length is restored to the new length.
+ //
+ let len = self.len();
+ let Range { start, end } = slice::range(range, ..len);
+
+ unsafe {
+ // set self.vec length's to start, to be safe in case Drain is leaked
+ self.set_len(start);
+ let range_slice = slice::from_raw_parts(self.as_ptr().add(start), end - start);
+ Drain {
+ tail_start: end,
+ tail_len: len - end,
+ iter: range_slice.iter(),
+ vec: NonNull::from(self),
+ }
+ }
+ }
+
+ /// Clears the vector, removing all values.
+ ///
+ /// Note that this method has no effect on the allocated capacity
+ /// of the vector.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut v = vec![1, 2, 3];
+ ///
+ /// v.clear();
+ ///
+ /// assert!(v.is_empty());
+ /// ```
+ #[inline]
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn clear(&mut self) {
+ let elems: *mut [T] = self.as_mut_slice();
+
+ // SAFETY:
+ // - `elems` comes directly from `as_mut_slice` and is therefore valid.
+ // - Setting `self.len` before calling `drop_in_place` means that,
+ // if an element's `Drop` impl panics, the vector's `Drop` impl will
+ // do nothing (leaking the rest of the elements) instead of dropping
+ // some twice.
+ unsafe {
+ self.len = 0;
+ ptr::drop_in_place(elems);
+ }
+ }
+
+ /// Returns the number of elements in the vector, also referred to
+ /// as its 'length'.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let a = vec![1, 2, 3];
+ /// assert_eq!(a.len(), 3);
+ /// ```
+ #[inline]
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn len(&self) -> usize {
+ self.len
+ }
+
+ /// Returns `true` if the vector contains no elements.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut v = Vec::new();
+ /// assert!(v.is_empty());
+ ///
+ /// v.push(1);
+ /// assert!(!v.is_empty());
+ /// ```
+ #[stable(feature = "rust1", since = "1.0.0")]
+ pub fn is_empty(&self) -> bool {
+ self.len() == 0
+ }
+
+ /// Splits the collection into two at the given index.
+ ///
+ /// Returns a newly allocated vector containing the elements in the range
+ /// `[at, len)`. After the call, the original vector will be left containing
+ /// the elements `[0, at)` with its previous capacity unchanged.
+ ///
+ /// # Panics
+ ///
+ /// Panics if `at > len`.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec![1, 2, 3];
+ /// let vec2 = vec.split_off(1);
+ /// assert_eq!(vec, [1]);
+ /// assert_eq!(vec2, [2, 3]);
+ /// ```
+ #[cfg(not(no_global_oom_handling))]
+ #[inline]
+ #[must_use = "use `.truncate()` if you don't need the other half"]
+ #[stable(feature = "split_off", since = "1.4.0")]
+ pub fn split_off(&mut self, at: usize) -> Self
+ where
+ A: Clone,
+ {
+ #[cold]
+ #[inline(never)]
+ fn assert_failed(at: usize, len: usize) -> ! {
+ panic!("`at` split index (is {at}) should be <= len (is {len})");
+ }
+
+ if at > self.len() {
+ assert_failed(at, self.len());
+ }
+
+ if at == 0 {
+ // the new vector can take over the original buffer and avoid the copy
+ return mem::replace(
+ self,
+ Vec::with_capacity_in(self.capacity(), self.allocator().clone()),
+ );
+ }
+
+ let other_len = self.len - at;
+ let mut other = Vec::with_capacity_in(other_len, self.allocator().clone());
+
+ // Unsafely `set_len` and copy items to `other`.
+ unsafe {
+ self.set_len(at);
+ other.set_len(other_len);
+
+ ptr::copy_nonoverlapping(self.as_ptr().add(at), other.as_mut_ptr(), other.len());
+ }
+ other
+ }
+
+ /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
+ ///
+ /// If `new_len` is greater than `len`, the `Vec` is extended by the
+ /// difference, with each additional slot filled with the result of
+ /// calling the closure `f`. The return values from `f` will end up
+ /// in the `Vec` in the order they have been generated.
+ ///
+ /// If `new_len` is less than `len`, the `Vec` is simply truncated.
+ ///
+ /// This method uses a closure to create new values on every push. If
+ /// you'd rather [`Clone`] a given value, use [`Vec::resize`]. If you
+ /// want to use the [`Default`] trait to generate values, you can
+ /// pass [`Default::default`] as the second argument.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec![1, 2, 3];
+ /// vec.resize_with(5, Default::default);
+ /// assert_eq!(vec, [1, 2, 3, 0, 0]);
+ ///
+ /// let mut vec = vec![];
+ /// let mut p = 1;
+ /// vec.resize_with(4, || { p *= 2; p });
+ /// assert_eq!(vec, [2, 4, 8, 16]);
+ /// ```
+ #[cfg(not(no_global_oom_handling))]
+ #[stable(feature = "vec_resize_with", since = "1.33.0")]
+ pub fn resize_with<F>(&mut self, new_len: usize, f: F)
+ where
+ F: FnMut() -> T,
+ {
+ let len = self.len();
+ if new_len > len {
+ self.extend_trusted(iter::repeat_with(f).take(new_len - len));
+ } else {
+ self.truncate(new_len);
+ }
+ }
+
+ /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
+ /// `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime
+ /// `'a`. If the type has only static references, or none at all, then this
+ /// may be chosen to be `'static`.
+ ///
+ /// As of Rust 1.57, this method does not reallocate or shrink the `Vec`,
+ /// so the leaked allocation may include unused capacity that is not part
+ /// of the returned slice.
+ ///
+ /// This function is mainly useful for data that lives for the remainder of
+ /// the program's life. Dropping the returned reference will cause a memory
+ /// leak.
+ ///
+ /// # Examples
+ ///
+ /// Simple usage:
+ ///
+ /// ```
+ /// let x = vec![1, 2, 3];
+ /// let static_ref: &'static mut [usize] = x.leak();
+ /// static_ref[0] += 1;
+ /// assert_eq!(static_ref, &[2, 2, 3]);
+ /// ```
+ #[stable(feature = "vec_leak", since = "1.47.0")]
+ #[inline]
+ pub fn leak<'a>(self) -> &'a mut [T]
+ where
+ A: 'a,
+ {
+ let mut me = ManuallyDrop::new(self);
+ unsafe { slice::from_raw_parts_mut(me.as_mut_ptr(), me.len) }
+ }
+
+ /// Returns the remaining spare capacity of the vector as a slice of
+ /// `MaybeUninit<T>`.
+ ///
+ /// The returned slice can be used to fill the vector with data (e.g. by
+ /// reading from a file) before marking the data as initialized using the
+ /// [`set_len`] method.
+ ///
+ /// [`set_len`]: Vec::set_len
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// // Allocate vector big enough for 10 elements.
+ /// let mut v = Vec::with_capacity(10);
+ ///
+ /// // Fill in the first 3 elements.
+ /// let uninit = v.spare_capacity_mut();
+ /// uninit[0].write(0);
+ /// uninit[1].write(1);
+ /// uninit[2].write(2);
+ ///
+ /// // Mark the first 3 elements of the vector as being initialized.
+ /// unsafe {
+ /// v.set_len(3);
+ /// }
+ ///
+ /// assert_eq!(&v, &[0, 1, 2]);
+ /// ```
+ #[stable(feature = "vec_spare_capacity", since = "1.60.0")]
+ #[inline]
+ pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
+ // Note:
+ // This method is not implemented in terms of `split_at_spare_mut`,
+ // to prevent invalidation of pointers to the buffer.
+ unsafe {
+ slice::from_raw_parts_mut(
+ self.as_mut_ptr().add(self.len) as *mut MaybeUninit<T>,
+ self.buf.capacity() - self.len,
+ )
+ }
+ }
+
+ /// Returns vector content as a slice of `T`, along with the remaining spare
+ /// capacity of the vector as a slice of `MaybeUninit<T>`.
+ ///
+ /// The returned spare capacity slice can be used to fill the vector with data
+ /// (e.g. by reading from a file) before marking the data as initialized using
+ /// the [`set_len`] method.
+ ///
+ /// [`set_len`]: Vec::set_len
+ ///
+ /// Note that this is a low-level API, which should be used with care for
+ /// optimization purposes. If you need to append data to a `Vec`
+ /// you can use [`push`], [`extend`], [`extend_from_slice`],
+ /// [`extend_from_within`], [`insert`], [`append`], [`resize`] or
+ /// [`resize_with`], depending on your exact needs.
+ ///
+ /// [`push`]: Vec::push
+ /// [`extend`]: Vec::extend
+ /// [`extend_from_slice`]: Vec::extend_from_slice
+ /// [`extend_from_within`]: Vec::extend_from_within
+ /// [`insert`]: Vec::insert
+ /// [`append`]: Vec::append
+ /// [`resize`]: Vec::resize
+ /// [`resize_with`]: Vec::resize_with
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// #![feature(vec_split_at_spare)]
+ ///
+ /// let mut v = vec![1, 1, 2];
+ ///
+ /// // Reserve additional space big enough for 10 elements.
+ /// v.reserve(10);
+ ///
+ /// let (init, uninit) = v.split_at_spare_mut();
+ /// let sum = init.iter().copied().sum::<u32>();
+ ///
+ /// // Fill in the next 4 elements.
+ /// uninit[0].write(sum);
+ /// uninit[1].write(sum * 2);
+ /// uninit[2].write(sum * 3);
+ /// uninit[3].write(sum * 4);
+ ///
+ /// // Mark the 4 elements of the vector as being initialized.
+ /// unsafe {
+ /// let len = v.len();
+ /// v.set_len(len + 4);
+ /// }
+ ///
+ /// assert_eq!(&v, &[1, 1, 2, 4, 8, 12, 16]);
+ /// ```
+ #[unstable(feature = "vec_split_at_spare", issue = "81944")]
+ #[inline]
+ pub fn split_at_spare_mut(&mut self) -> (&mut [T], &mut [MaybeUninit<T>]) {
+ // SAFETY:
+ // - len is ignored and so never changed
+ let (init, spare, _) = unsafe { self.split_at_spare_mut_with_len() };
+ (init, spare)
+ }
+
+ /// Safety: changing returned .2 (&mut usize) is considered the same as calling `.set_len(_)`.
+ ///
+ /// This method provides unique access to all vec parts at once in `extend_from_within`.
+ unsafe fn split_at_spare_mut_with_len(
+ &mut self,
+ ) -> (&mut [T], &mut [MaybeUninit<T>], &mut usize) {
+ let ptr = self.as_mut_ptr();
+ // SAFETY:
+ // - `ptr` is guaranteed to be valid for `self.len` elements
+ // - but the allocation extends out to `self.buf.capacity()` elements, possibly
+ // uninitialized
+ let spare_ptr = unsafe { ptr.add(self.len) };
+ let spare_ptr = spare_ptr.cast::<MaybeUninit<T>>();
+ let spare_len = self.buf.capacity() - self.len;
+
+ // SAFETY:
+ // - `ptr` is guaranteed to be valid for `self.len` elements
+ // - `spare_ptr` is pointing one element past the buffer, so it doesn't overlap with `initialized`
+ unsafe {
+ let initialized = slice::from_raw_parts_mut(ptr, self.len);
+ let spare = slice::from_raw_parts_mut(spare_ptr, spare_len);
+
+ (initialized, spare, &mut self.len)
+ }
+ }
+}
+
+impl<T: Clone, A: Allocator> Vec<T, A> {
+ /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
+ ///
+ /// If `new_len` is greater than `len`, the `Vec` is extended by the
+ /// difference, with each additional slot filled with `value`.
+ /// If `new_len` is less than `len`, the `Vec` is simply truncated.
+ ///
+ /// This method requires `T` to implement [`Clone`],
+ /// in order to be able to clone the passed value.
+ /// If you need more flexibility (or want to rely on [`Default`] instead of
+ /// [`Clone`]), use [`Vec::resize_with`].
+ /// If you only need to resize to a smaller size, use [`Vec::truncate`].
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec!["hello"];
+ /// vec.resize(3, "world");
+ /// assert_eq!(vec, ["hello", "world", "world"]);
+ ///
+ /// let mut vec = vec![1, 2, 3, 4];
+ /// vec.resize(2, 0);
+ /// assert_eq!(vec, [1, 2]);
+ /// ```
+ #[cfg(not(no_global_oom_handling))]
+ #[stable(feature = "vec_resize", since = "1.5.0")]
+ pub fn resize(&mut self, new_len: usize, value: T) {
+ let len = self.len();
+
+ if new_len > len {
+ self.extend_with(new_len - len, ExtendElement(value))
+ } else {
+ self.truncate(new_len);
+ }
+ }
+
+ /// Tries to resize the `Vec` in-place so that `len` is equal to `new_len`.
+ ///
+ /// If `new_len` is greater than `len`, the `Vec` is extended by the
+ /// difference, with each additional slot filled with `value`.
+ /// If `new_len` is less than `len`, the `Vec` is simply truncated.
+ ///
+ /// This method requires `T` to implement [`Clone`],
+ /// in order to be able to clone the passed value.
+ /// If you need more flexibility (or want to rely on [`Default`] instead of
+ /// [`Clone`]), use [`Vec::resize_with`].
+ /// If you only need to resize to a smaller size, use [`Vec::truncate`].
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec!["hello"];
+ /// vec.try_resize(3, "world").unwrap();
+ /// assert_eq!(vec, ["hello", "world", "world"]);
+ ///
+ /// let mut vec = vec![1, 2, 3, 4];
+ /// vec.try_resize(2, 0).unwrap();
+ /// assert_eq!(vec, [1, 2]);
+ ///
+ /// let mut vec = vec![42];
+ /// let result = vec.try_resize(usize::MAX, 0);
+ /// assert!(result.is_err());
+ /// ```
+ #[stable(feature = "kernel", since = "1.0.0")]
+ pub fn try_resize(&mut self, new_len: usize, value: T) -> Result<(), TryReserveError> {
+ let len = self.len();
+
+ if new_len > len {
+ self.try_extend_with(new_len - len, ExtendElement(value))
+ } else {
+ self.truncate(new_len);
+ Ok(())
+ }
+ }
+
+ /// Clones and appends all elements in a slice to the `Vec`.
+ ///
+ /// Iterates over the slice `other`, clones each element, and then appends
+ /// it to this `Vec`. The `other` slice is traversed in-order.
+ ///
+ /// Note that this function is same as [`extend`] except that it is
+ /// specialized to work with slices instead. If and when Rust gets
+ /// specialization this function will likely be deprecated (but still
+ /// available).
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec![1];
+ /// vec.extend_from_slice(&[2, 3, 4]);
+ /// assert_eq!(vec, [1, 2, 3, 4]);
+ /// ```
+ ///
+ /// [`extend`]: Vec::extend
+ #[cfg(not(no_global_oom_handling))]
+ #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
+ pub fn extend_from_slice(&mut self, other: &[T]) {
+ self.spec_extend(other.iter())
+ }
+
+ /// Tries to clone and append all elements in a slice to the `Vec`.
+ ///
+ /// Iterates over the slice `other`, clones each element, and then appends
+ /// it to this `Vec`. The `other` slice is traversed in-order.
+ ///
+ /// Note that this function is same as [`extend`] except that it is
+ /// specialized to work with slices instead. If and when Rust gets
+ /// specialization this function will likely be deprecated (but still
+ /// available).
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec![1];
+ /// vec.try_extend_from_slice(&[2, 3, 4]).unwrap();
+ /// assert_eq!(vec, [1, 2, 3, 4]);
+ /// ```
+ ///
+ /// [`extend`]: Vec::extend
+ #[stable(feature = "kernel", since = "1.0.0")]
+ pub fn try_extend_from_slice(&mut self, other: &[T]) -> Result<(), TryReserveError> {
+ self.try_spec_extend(other.iter())
+ }
+
+ /// Copies elements from `src` range to the end of the vector.
+ ///
+ /// # Panics
+ ///
+ /// Panics if the starting point is greater than the end point or if
+ /// the end point is greater than the length of the vector.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec![0, 1, 2, 3, 4];
+ ///
+ /// vec.extend_from_within(2..);
+ /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]);
+ ///
+ /// vec.extend_from_within(..2);
+ /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]);
+ ///
+ /// vec.extend_from_within(4..8);
+ /// assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);
+ /// ```
+ #[cfg(not(no_global_oom_handling))]
+ #[stable(feature = "vec_extend_from_within", since = "1.53.0")]
+ pub fn extend_from_within<R>(&mut self, src: R)
+ where
+ R: RangeBounds<usize>,
+ {
+ let range = slice::range(src, ..self.len());
+ self.reserve(range.len());
+
+ // SAFETY:
+ // - `slice::range` guarantees that the given range is valid for indexing self
+ unsafe {
+ self.spec_extend_from_within(range);
+ }
+ }
+}
+
+impl<T, A: Allocator, const N: usize> Vec<[T; N], A> {
+ /// Takes a `Vec<[T; N]>` and flattens it into a `Vec<T>`.
+ ///
+ /// # Panics
+ ///
+ /// Panics if the length of the resulting vector would overflow a `usize`.
+ ///
+ /// This is only possible when flattening a vector of arrays of zero-sized
+ /// types, and thus tends to be irrelevant in practice. If
+ /// `size_of::<T>() > 0`, this will never panic.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// #![feature(slice_flatten)]
+ ///
+ /// let mut vec = vec![[1, 2, 3], [4, 5, 6], [7, 8, 9]];
+ /// assert_eq!(vec.pop(), Some([7, 8, 9]));
+ ///
+ /// let mut flattened = vec.into_flattened();
+ /// assert_eq!(flattened.pop(), Some(6));
+ /// ```
+ #[unstable(feature = "slice_flatten", issue = "95629")]
+ pub fn into_flattened(self) -> Vec<T, A> {
+ let (ptr, len, cap, alloc) = self.into_raw_parts_with_alloc();
+ let (new_len, new_cap) = if T::IS_ZST {
+ (len.checked_mul(N).expect("vec len overflow"), usize::MAX)
+ } else {
+ // SAFETY:
+ // - `cap * N` cannot overflow because the allocation is already in
+ // the address space.
+ // - Each `[T; N]` has `N` valid elements, so there are `len * N`
+ // valid elements in the allocation.
+ unsafe { (len.unchecked_mul(N), cap.unchecked_mul(N)) }
+ };
+ // SAFETY:
+ // - `ptr` was allocated by `self`
+ // - `ptr` is well-aligned because `[T; N]` has the same alignment as `T`.
+ // - `new_cap` refers to the same sized allocation as `cap` because
+ // `new_cap * size_of::<T>()` == `cap * size_of::<[T; N]>()`
+ // - `len` <= `cap`, so `len * N` <= `cap * N`.
+ unsafe { Vec::<T, A>::from_raw_parts_in(ptr.cast(), new_len, new_cap, alloc) }
+ }
+}
+
+// This code generalizes `extend_with_{element,default}`.
+trait ExtendWith<T> {
+ fn next(&mut self) -> T;
+ fn last(self) -> T;
+}
+
+struct ExtendElement<T>(T);
+impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
+ fn next(&mut self) -> T {
+ self.0.clone()
+ }
+ fn last(self) -> T {
+ self.0
+ }
+}
+
+impl<T, A: Allocator> Vec<T, A> {
+ #[cfg(not(no_global_oom_handling))]
+ /// Extend the vector by `n` values, using the given generator.
+ fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
+ self.reserve(n);
+
+ unsafe {
+ let mut ptr = self.as_mut_ptr().add(self.len());
+ // Use SetLenOnDrop to work around bug where compiler
+ // might not realize the store through `ptr` through self.set_len()
+ // don't alias.
+ let mut local_len = SetLenOnDrop::new(&mut self.len);
+
+ // Write all elements except the last one
+ for _ in 1..n {
+ ptr::write(ptr, value.next());
+ ptr = ptr.add(1);
+ // Increment the length in every step in case next() panics
+ local_len.increment_len(1);
+ }
+
+ if n > 0 {
+ // We can write the last element directly without cloning needlessly
+ ptr::write(ptr, value.last());
+ local_len.increment_len(1);
+ }
+
+ // len set by scope guard
+ }
+ }
+
+ /// Try to extend the vector by `n` values, using the given generator.
+ fn try_extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) -> Result<(), TryReserveError> {
+ self.try_reserve(n)?;
+
+ unsafe {
+ let mut ptr = self.as_mut_ptr().add(self.len());
+ // Use SetLenOnDrop to work around bug where compiler
+ // might not realize the store through `ptr` through self.set_len()
+ // don't alias.
+ let mut local_len = SetLenOnDrop::new(&mut self.len);
+
+ // Write all elements except the last one
+ for _ in 1..n {
+ ptr::write(ptr, value.next());
+ ptr = ptr.add(1);
+ // Increment the length in every step in case next() panics
+ local_len.increment_len(1);
+ }
+
+ if n > 0 {
+ // We can write the last element directly without cloning needlessly
+ ptr::write(ptr, value.last());
+ local_len.increment_len(1);
+ }
+
+ // len set by scope guard
+ Ok(())
+ }
+ }
+}
+
+impl<T: PartialEq, A: Allocator> Vec<T, A> {
+ /// Removes consecutive repeated elements in the vector according to the
+ /// [`PartialEq`] trait implementation.
+ ///
+ /// If the vector is sorted, this removes all duplicates.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut vec = vec![1, 2, 2, 3, 2];
+ ///
+ /// vec.dedup();
+ ///
+ /// assert_eq!(vec, [1, 2, 3, 2]);
+ /// ```
+ #[stable(feature = "rust1", since = "1.0.0")]
+ #[inline]
+ pub fn dedup(&mut self) {
+ self.dedup_by(|a, b| a == b)
+ }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Internal methods and functions
+////////////////////////////////////////////////////////////////////////////////
+
+#[doc(hidden)]
+#[cfg(not(no_global_oom_handling))]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
+ <T as SpecFromElem>::from_elem(elem, n, Global)
+}
+
+#[doc(hidden)]
+#[cfg(not(no_global_oom_handling))]
+#[unstable(feature = "allocator_api", issue = "32838")]
+pub fn from_elem_in<T: Clone, A: Allocator>(elem: T, n: usize, alloc: A) -> Vec<T, A> {
+ <T as SpecFromElem>::from_elem(elem, n, alloc)
+}
+
+trait ExtendFromWithinSpec {
+ /// # Safety
+ ///
+ /// - `src` needs to be valid index
+ /// - `self.capacity() - self.len()` must be `>= src.len()`
+ unsafe fn spec_extend_from_within(&mut self, src: Range<usize>);
+}
+
+impl<T: Clone, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
+ default unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
+ // SAFETY:
+ // - len is increased only after initializing elements
+ let (this, spare, len) = unsafe { self.split_at_spare_mut_with_len() };
+
+ // SAFETY:
+ // - caller guarantees that src is a valid index
+ let to_clone = unsafe { this.get_unchecked(src) };
+
+ iter::zip(to_clone, spare)
+ .map(|(src, dst)| dst.write(src.clone()))
+ // Note:
+ // - Element was just initialized with `MaybeUninit::write`, so it's ok to increase len
+ // - len is increased after each element to prevent leaks (see issue #82533)
+ .for_each(|_| *len += 1);
+ }
+}
+
+impl<T: Copy, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
+ unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
+ let count = src.len();
+ {
+ let (init, spare) = self.split_at_spare_mut();
+
+ // SAFETY:
+ // - caller guarantees that `src` is a valid index
+ let source = unsafe { init.get_unchecked(src) };
+
+ // SAFETY:
+ // - Both pointers are created from unique slice references (`&mut [_]`)
+ // so they are valid and do not overlap.
+ // - Elements are :Copy so it's OK to copy them, without doing
+ // anything with the original values
+ // - `count` is equal to the len of `source`, so source is valid for
+ // `count` reads
+ // - `.reserve(count)` guarantees that `spare.len() >= count` so spare
+ // is valid for `count` writes
+ unsafe { ptr::copy_nonoverlapping(source.as_ptr(), spare.as_mut_ptr() as _, count) };
+ }
+
+ // SAFETY:
+ // - The elements were just initialized by `copy_nonoverlapping`
+ self.len += count;
+ }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Common trait implementations for Vec
+////////////////////////////////////////////////////////////////////////////////
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T, A: Allocator> ops::Deref for Vec<T, A> {
+ type Target = [T];
+
+ #[inline]
+ fn deref(&self) -> &[T] {
+ unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T, A: Allocator> ops::DerefMut for Vec<T, A> {
+ #[inline]
+ fn deref_mut(&mut self) -> &mut [T] {
+ unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
+ }
+}
+
+#[cfg(not(no_global_oom_handling))]
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
+ #[cfg(not(test))]
+ fn clone(&self) -> Self {
+ let alloc = self.allocator().clone();
+ <[T]>::to_vec_in(&**self, alloc)
+ }
+
+ // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
+ // required for this method definition, is not available. Instead use the
+ // `slice::to_vec` function which is only available with cfg(test)
+ // NB see the slice::hack module in slice.rs for more information
+ #[cfg(test)]
+ fn clone(&self) -> Self {
+ let alloc = self.allocator().clone();
+ crate::slice::to_vec(&**self, alloc)
+ }
+
+ fn clone_from(&mut self, other: &Self) {
+ crate::slice::SpecCloneIntoVec::clone_into(other.as_slice(), self);
+ }
+}
+
+/// The hash of a vector is the same as that of the corresponding slice,
+/// as required by the `core::borrow::Borrow` implementation.
+///
+/// ```
+/// use std::hash::BuildHasher;
+///
+/// let b = std::collections::hash_map::RandomState::new();
+/// let v: Vec<u8> = vec![0xa8, 0x3c, 0x09];
+/// let s: &[u8] = &[0xa8, 0x3c, 0x09];
+/// assert_eq!(b.hash_one(v), b.hash_one(s));
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Hash, A: Allocator> Hash for Vec<T, A> {
+ #[inline]
+ fn hash<H: Hasher>(&self, state: &mut H) {
+ Hash::hash(&**self, state)
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_on_unimplemented(
+ message = "vector indices are of type `usize` or ranges of `usize`",
+ label = "vector indices are of type `usize` or ranges of `usize`"
+)]
+impl<T, I: SliceIndex<[T]>, A: Allocator> Index<I> for Vec<T, A> {
+ type Output = I::Output;
+
+ #[inline]
+ fn index(&self, index: I) -> &Self::Output {
+ Index::index(&**self, index)
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_on_unimplemented(
+ message = "vector indices are of type `usize` or ranges of `usize`",
+ label = "vector indices are of type `usize` or ranges of `usize`"
+)]
+impl<T, I: SliceIndex<[T]>, A: Allocator> IndexMut<I> for Vec<T, A> {
+ #[inline]
+ fn index_mut(&mut self, index: I) -> &mut Self::Output {
+ IndexMut::index_mut(&mut **self, index)
+ }
+}
+
+#[cfg(not(no_global_oom_handling))]
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> FromIterator<T> for Vec<T> {
+ #[inline]
+ fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
+ <Self as SpecFromIter<T, I::IntoIter>>::from_iter(iter.into_iter())
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T, A: Allocator> IntoIterator for Vec<T, A> {
+ type Item = T;
+ type IntoIter = IntoIter<T, A>;
+
+ /// Creates a consuming iterator, that is, one that moves each value out of
+ /// the vector (from start to end). The vector cannot be used after calling
+ /// this.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let v = vec!["a".to_string(), "b".to_string()];
+ /// let mut v_iter = v.into_iter();
+ ///
+ /// let first_element: Option<String> = v_iter.next();
+ ///
+ /// assert_eq!(first_element, Some("a".to_string()));
+ /// assert_eq!(v_iter.next(), Some("b".to_string()));
+ /// assert_eq!(v_iter.next(), None);
+ /// ```
+ #[inline]
+ fn into_iter(self) -> Self::IntoIter {
+ unsafe {
+ let mut me = ManuallyDrop::new(self);
+ let alloc = ManuallyDrop::new(ptr::read(me.allocator()));
+ let begin = me.as_mut_ptr();
+ let end = if T::IS_ZST {
+ begin.wrapping_byte_add(me.len())
+ } else {
+ begin.add(me.len()) as *const T
+ };
+ let cap = me.buf.capacity();
+ IntoIter {
+ buf: NonNull::new_unchecked(begin),
+ phantom: PhantomData,
+ cap,
+ alloc,
+ ptr: begin,
+ end,
+ }
+ }
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T, A: Allocator> IntoIterator for &'a Vec<T, A> {
+ type Item = &'a T;
+ type IntoIter = slice::Iter<'a, T>;
+
+ fn into_iter(self) -> Self::IntoIter {
+ self.iter()
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T, A: Allocator> IntoIterator for &'a mut Vec<T, A> {
+ type Item = &'a mut T;
+ type IntoIter = slice::IterMut<'a, T>;
+
+ fn into_iter(self) -> Self::IntoIter {
+ self.iter_mut()
+ }
+}
+
+#[cfg(not(no_global_oom_handling))]
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T, A: Allocator> Extend<T> for Vec<T, A> {
+ #[inline]
+ fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
+ <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
+ }
+
+ #[inline]
+ fn extend_one(&mut self, item: T) {
+ self.push(item);
+ }
+
+ #[inline]
+ fn extend_reserve(&mut self, additional: usize) {
+ self.reserve(additional);
+ }
+}
+
+impl<T, A: Allocator> Vec<T, A> {
+ // leaf method to which various SpecFrom/SpecExtend implementations delegate when
+ // they have no further optimizations to apply
+ #[cfg(not(no_global_oom_handling))]
+ fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
+ // This is the case for a general iterator.
+ //
+ // This function should be the moral equivalent of:
+ //
+ // for item in iterator {
+ // self.push(item);
+ // }
+ while let Some(element) = iterator.next() {
+ let len = self.len();
+ if len == self.capacity() {
+ let (lower, _) = iterator.size_hint();
+ self.reserve(lower.saturating_add(1));
+ }
+ unsafe {
+ ptr::write(self.as_mut_ptr().add(len), element);
+ // Since next() executes user code which can panic we have to bump the length
+ // after each step.
+ // NB can't overflow since we would have had to alloc the address space
+ self.set_len(len + 1);
+ }
+ }
+ }
+
+ // leaf method to which various SpecFrom/SpecExtend implementations delegate when
+ // they have no further optimizations to apply
+ fn try_extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) -> Result<(), TryReserveError> {
+ // This is the case for a general iterator.
+ //
+ // This function should be the moral equivalent of:
+ //
+ // for item in iterator {
+ // self.push(item);
+ // }
+ while let Some(element) = iterator.next() {
+ let len = self.len();
+ if len == self.capacity() {
+ let (lower, _) = iterator.size_hint();
+ self.try_reserve(lower.saturating_add(1))?;
+ }
+ unsafe {
+ ptr::write(self.as_mut_ptr().add(len), element);
+ // Since next() executes user code which can panic we have to bump the length
+ // after each step.
+ // NB can't overflow since we would have had to alloc the address space
+ self.set_len(len + 1);
+ }
+ }
+
+ Ok(())
+ }
+
+ // specific extend for `TrustedLen` iterators, called both by the specializations
+ // and internal places where resolving specialization makes compilation slower
+ #[cfg(not(no_global_oom_handling))]
+ fn extend_trusted(&mut self, iterator: impl iter::TrustedLen<Item = T>) {
+ let (low, high) = iterator.size_hint();
+ if let Some(additional) = high {
+ debug_assert_eq!(
+ low,
+ additional,
+ "TrustedLen iterator's size hint is not exact: {:?}",
+ (low, high)
+ );
+ self.reserve(additional);
+ unsafe {
+ let ptr = self.as_mut_ptr();
+ let mut local_len = SetLenOnDrop::new(&mut self.len);
+ iterator.for_each(move |element| {
+ ptr::write(ptr.add(local_len.current_len()), element);
+ // Since the loop executes user code which can panic we have to update
+ // the length every step to correctly drop what we've written.
+ // NB can't overflow since we would have had to alloc the address space
+ local_len.increment_len(1);
+ });
+ }
+ } else {
+ // Per TrustedLen contract a `None` upper bound means that the iterator length
+ // truly exceeds usize::MAX, which would eventually lead to a capacity overflow anyway.
+ // Since the other branch already panics eagerly (via `reserve()`) we do the same here.
+ // This avoids additional codegen for a fallback code path which would eventually
+ // panic anyway.
+ panic!("capacity overflow");
+ }
+ }
+
+ // specific extend for `TrustedLen` iterators, called both by the specializations
+ // and internal places where resolving specialization makes compilation slower
+ fn try_extend_trusted(&mut self, iterator: impl iter::TrustedLen<Item = T>) -> Result<(), TryReserveError> {
+ let (low, high) = iterator.size_hint();
+ if let Some(additional) = high {
+ debug_assert_eq!(
+ low,
+ additional,
+ "TrustedLen iterator's size hint is not exact: {:?}",
+ (low, high)
+ );
+ self.try_reserve(additional)?;
+ unsafe {
+ let ptr = self.as_mut_ptr();
+ let mut local_len = SetLenOnDrop::new(&mut self.len);
+ iterator.for_each(move |element| {
+ ptr::write(ptr.add(local_len.current_len()), element);
+ // Since the loop executes user code which can panic we have to update
+ // the length every step to correctly drop what we've written.
+ // NB can't overflow since we would have had to alloc the address space
+ local_len.increment_len(1);
+ });
+ }
+ Ok(())
+ } else {
+ Err(TryReserveErrorKind::CapacityOverflow.into())
+ }
+ }
+
+ /// Creates a splicing iterator that replaces the specified range in the vector
+ /// with the given `replace_with` iterator and yields the removed items.
+ /// `replace_with` does not need to be the same length as `range`.
+ ///
+ /// `range` is removed even if the iterator is not consumed until the end.
+ ///
+ /// It is unspecified how many elements are removed from the vector
+ /// if the `Splice` value is leaked.
+ ///
+ /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
+ ///
+ /// This is optimal if:
+ ///
+ /// * The tail (elements in the vector after `range`) is empty,
+ /// * or `replace_with` yields fewer or equal elements than `range`’s length
+ /// * or the lower bound of its `size_hint()` is exact.
+ ///
+ /// Otherwise, a temporary vector is allocated and the tail is moved twice.
+ ///
+ /// # Panics
+ ///
+ /// Panics if the starting point is greater than the end point or if
+ /// the end point is greater than the length of the vector.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut v = vec![1, 2, 3, 4];
+ /// let new = [7, 8, 9];
+ /// let u: Vec<_> = v.splice(1..3, new).collect();
+ /// assert_eq!(v, &[1, 7, 8, 9, 4]);
+ /// assert_eq!(u, &[2, 3]);
+ /// ```
+ #[cfg(not(no_global_oom_handling))]
+ #[inline]
+ #[stable(feature = "vec_splice", since = "1.21.0")]
+ pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter, A>
+ where
+ R: RangeBounds<usize>,
+ I: IntoIterator<Item = T>,
+ {
+ Splice { drain: self.drain(range), replace_with: replace_with.into_iter() }
+ }
+
+ /// Creates an iterator which uses a closure to determine if an element should be removed.
+ ///
+ /// If the closure returns true, then the element is removed and yielded.
+ /// If the closure returns false, the element will remain in the vector and will not be yielded
+ /// by the iterator.
+ ///
+ /// Using this method is equivalent to the following code:
+ ///
+ /// ```
+ /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
+ /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
+ /// let mut i = 0;
+ /// while i < vec.len() {
+ /// if some_predicate(&mut vec[i]) {
+ /// let val = vec.remove(i);
+ /// // your code here
+ /// } else {
+ /// i += 1;
+ /// }
+ /// }
+ ///
+ /// # assert_eq!(vec, vec![1, 4, 5]);
+ /// ```
+ ///
+ /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
+ /// because it can backshift the elements of the array in bulk.
+ ///
+ /// Note that `drain_filter` also lets you mutate every element in the filter closure,
+ /// regardless of whether you choose to keep or remove it.
+ ///
+ /// # Examples
+ ///
+ /// Splitting an array into evens and odds, reusing the original allocation:
+ ///
+ /// ```
+ /// #![feature(drain_filter)]
+ /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
+ ///
+ /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
+ /// let odds = numbers;
+ ///
+ /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
+ /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
+ /// ```
+ #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
+ pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F, A>
+ where
+ F: FnMut(&mut T) -> bool,
+ {
+ let old_len = self.len();
+
+ // Guard against us getting leaked (leak amplification)
+ unsafe {
+ self.set_len(0);
+ }
+
+ DrainFilter { vec: self, idx: 0, del: 0, old_len, pred: filter, panic_flag: false }
+ }
+}
+
+/// Extend implementation that copies elements out of references before pushing them onto the Vec.
+///
+/// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
+/// append the entire slice at once.
+///
+/// [`copy_from_slice`]: slice::copy_from_slice
+#[cfg(not(no_global_oom_handling))]
+#[stable(feature = "extend_ref", since = "1.2.0")]
+impl<'a, T: Copy + 'a, A: Allocator + 'a> Extend<&'a T> for Vec<T, A> {
+ fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
+ self.spec_extend(iter.into_iter())
+ }
+
+ #[inline]
+ fn extend_one(&mut self, &item: &'a T) {
+ self.push(item);
+ }
+
+ #[inline]
+ fn extend_reserve(&mut self, additional: usize) {
+ self.reserve(additional);
+ }
+}
+
+/// Implements comparison of vectors, [lexicographically](Ord#lexicographical-comparison).
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: PartialOrd, A: Allocator> PartialOrd for Vec<T, A> {
+ #[inline]
+ fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+ PartialOrd::partial_cmp(&**self, &**other)
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Eq, A: Allocator> Eq for Vec<T, A> {}
+
+/// Implements ordering of vectors, [lexicographically](Ord#lexicographical-comparison).
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Ord, A: Allocator> Ord for Vec<T, A> {
+ #[inline]
+ fn cmp(&self, other: &Self) -> Ordering {
+ Ord::cmp(&**self, &**other)
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
+ fn drop(&mut self) {
+ unsafe {
+ // use drop for [T]
+ // use a raw slice to refer to the elements of the vector as weakest necessary type;
+ // could avoid questions of validity in certain cases
+ ptr::drop_in_place(ptr::slice_from_raw_parts_mut(self.as_mut_ptr(), self.len))
+ }
+ // RawVec handles deallocation
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Default for Vec<T> {
+ /// Creates an empty `Vec<T>`.
+ ///
+ /// The vector will not allocate until elements are pushed onto it.
+ fn default() -> Vec<T> {
+ Vec::new()
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: fmt::Debug, A: Allocator> fmt::Debug for Vec<T, A> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ fmt::Debug::fmt(&**self, f)
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T, A: Allocator> AsRef<Vec<T, A>> for Vec<T, A> {
+ fn as_ref(&self) -> &Vec<T, A> {
+ self
+ }
+}
+
+#[stable(feature = "vec_as_mut", since = "1.5.0")]
+impl<T, A: Allocator> AsMut<Vec<T, A>> for Vec<T, A> {
+ fn as_mut(&mut self) -> &mut Vec<T, A> {
+ self
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T, A: Allocator> AsRef<[T]> for Vec<T, A> {
+ fn as_ref(&self) -> &[T] {
+ self
+ }
+}
+
+#[stable(feature = "vec_as_mut", since = "1.5.0")]
+impl<T, A: Allocator> AsMut<[T]> for Vec<T, A> {
+ fn as_mut(&mut self) -> &mut [T] {
+ self
+ }
+}
+
+#[cfg(not(no_global_oom_handling))]
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Clone> From<&[T]> for Vec<T> {
+ /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// assert_eq!(Vec::from(&[1, 2, 3][..]), vec![1, 2, 3]);
+ /// ```
+ #[cfg(not(test))]
+ fn from(s: &[T]) -> Vec<T> {
+ s.to_vec()
+ }
+ #[cfg(test)]
+ fn from(s: &[T]) -> Vec<T> {
+ crate::slice::to_vec(s, Global)
+ }
+}
+
+#[cfg(not(no_global_oom_handling))]
+#[stable(feature = "vec_from_mut", since = "1.19.0")]
+impl<T: Clone> From<&mut [T]> for Vec<T> {
+ /// Allocate a `Vec<T>` and fill it by cloning `s`'s items.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// assert_eq!(Vec::from(&mut [1, 2, 3][..]), vec![1, 2, 3]);
+ /// ```
+ #[cfg(not(test))]
+ fn from(s: &mut [T]) -> Vec<T> {
+ s.to_vec()
+ }
+ #[cfg(test)]
+ fn from(s: &mut [T]) -> Vec<T> {
+ crate::slice::to_vec(s, Global)
+ }
+}
+
+#[cfg(not(no_global_oom_handling))]
+#[stable(feature = "vec_from_array", since = "1.44.0")]
+impl<T, const N: usize> From<[T; N]> for Vec<T> {
+ /// Allocate a `Vec<T>` and move `s`'s items into it.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// assert_eq!(Vec::from([1, 2, 3]), vec![1, 2, 3]);
+ /// ```
+ #[cfg(not(test))]
+ fn from(s: [T; N]) -> Vec<T> {
+ <[T]>::into_vec(Box::new(s))
+ }
+
+ #[cfg(test)]
+ fn from(s: [T; N]) -> Vec<T> {
+ crate::slice::into_vec(Box::new(s))
+ }
+}
+
+#[cfg(not(no_borrow))]
+#[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
+impl<'a, T> From<Cow<'a, [T]>> for Vec<T>
+where
+ [T]: ToOwned<Owned = Vec<T>>,
+{
+ /// Convert a clone-on-write slice into a vector.
+ ///
+ /// If `s` already owns a `Vec<T>`, it will be returned directly.
+ /// If `s` is borrowing a slice, a new `Vec<T>` will be allocated and
+ /// filled by cloning `s`'s items into it.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// # use std::borrow::Cow;
+ /// let o: Cow<'_, [i32]> = Cow::Owned(vec![1, 2, 3]);
+ /// let b: Cow<'_, [i32]> = Cow::Borrowed(&[1, 2, 3]);
+ /// assert_eq!(Vec::from(o), Vec::from(b));
+ /// ```
+ fn from(s: Cow<'a, [T]>) -> Vec<T> {
+ s.into_owned()
+ }
+}
+
+// note: test pulls in std, which causes errors here
+#[cfg(not(test))]
+#[stable(feature = "vec_from_box", since = "1.18.0")]
+impl<T, A: Allocator> From<Box<[T], A>> for Vec<T, A> {
+ /// Convert a boxed slice into a vector by transferring ownership of
+ /// the existing heap allocation.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let b: Box<[i32]> = vec![1, 2, 3].into_boxed_slice();
+ /// assert_eq!(Vec::from(b), vec![1, 2, 3]);
+ /// ```
+ fn from(s: Box<[T], A>) -> Self {
+ s.into_vec()
+ }
+}
+
+// note: test pulls in std, which causes errors here
+#[cfg(not(no_global_oom_handling))]
+#[cfg(not(test))]
+#[stable(feature = "box_from_vec", since = "1.20.0")]
+impl<T, A: Allocator> From<Vec<T, A>> for Box<[T], A> {
+ /// Convert a vector into a boxed slice.
+ ///
+ /// If `v` has excess capacity, its items will be moved into a
+ /// newly-allocated buffer with exactly the right capacity.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// assert_eq!(Box::from(vec![1, 2, 3]), vec![1, 2, 3].into_boxed_slice());
+ /// ```
+ ///
+ /// Any excess capacity is removed:
+ /// ```
+ /// let mut vec = Vec::with_capacity(10);
+ /// vec.extend([1, 2, 3]);
+ ///
+ /// assert_eq!(Box::from(vec), vec![1, 2, 3].into_boxed_slice());
+ /// ```
+ fn from(v: Vec<T, A>) -> Self {
+ v.into_boxed_slice()
+ }
+}
+
+#[cfg(not(no_global_oom_handling))]
+#[stable(feature = "rust1", since = "1.0.0")]
+impl From<&str> for Vec<u8> {
+ /// Allocate a `Vec<u8>` and fill it with a UTF-8 string.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// assert_eq!(Vec::from("123"), vec![b'1', b'2', b'3']);
+ /// ```
+ fn from(s: &str) -> Vec<u8> {
+ From::from(s.as_bytes())
+ }
+}
+
+#[stable(feature = "array_try_from_vec", since = "1.48.0")]
+impl<T, A: Allocator, const N: usize> TryFrom<Vec<T, A>> for [T; N] {
+ type Error = Vec<T, A>;
+
+ /// Gets the entire contents of the `Vec<T>` as an array,
+ /// if its size exactly matches that of the requested array.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// assert_eq!(vec![1, 2, 3].try_into(), Ok([1, 2, 3]));
+ /// assert_eq!(<Vec<i32>>::new().try_into(), Ok([]));
+ /// ```
+ ///
+ /// If the length doesn't match, the input comes back in `Err`:
+ /// ```
+ /// let r: Result<[i32; 4], _> = (0..10).collect::<Vec<_>>().try_into();
+ /// assert_eq!(r, Err(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));
+ /// ```
+ ///
+ /// If you're fine with just getting a prefix of the `Vec<T>`,
+ /// you can call [`.truncate(N)`](Vec::truncate) first.
+ /// ```
+ /// let mut v = String::from("hello world").into_bytes();
+ /// v.sort();
+ /// v.truncate(2);
+ /// let [a, b]: [_; 2] = v.try_into().unwrap();
+ /// assert_eq!(a, b' ');
+ /// assert_eq!(b, b'd');
+ /// ```
+ fn try_from(mut vec: Vec<T, A>) -> Result<[T; N], Vec<T, A>> {
+ if vec.len() != N {
+ return Err(vec);
+ }
+
+ // SAFETY: `.set_len(0)` is always sound.
+ unsafe { vec.set_len(0) };
+
+ // SAFETY: A `Vec`'s pointer is always aligned properly, and
+ // the alignment the array needs is the same as the items.
+ // We checked earlier that we have sufficient items.
+ // The items will not double-drop as the `set_len`
+ // tells the `Vec` not to also drop them.
+ let array = unsafe { ptr::read(vec.as_ptr() as *const [T; N]) };
+ Ok(array)
+ }
+}