diff options
Diffstat (limited to '')
| -rw-r--r-- | library/alloc/src/vec/mod.rs | 144 |
1 files changed, 126 insertions, 18 deletions
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs index 60b36af5e..bbbdc3aa2 100644 --- a/library/alloc/src/vec/mod.rs +++ b/library/alloc/src/vec/mod.rs @@ -64,7 +64,7 @@ use core::iter; #[cfg(not(no_global_oom_handling))] use core::iter::FromIterator; use core::marker::PhantomData; -use core::mem::{self, ManuallyDrop, MaybeUninit}; +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}; @@ -125,7 +125,7 @@ use self::set_len_on_drop::SetLenOnDrop; mod set_len_on_drop; #[cfg(not(no_global_oom_handling))] -use self::in_place_drop::InPlaceDrop; +use self::in_place_drop::{InPlaceDrop, InPlaceDstBufDrop}; #[cfg(not(no_global_oom_handling))] mod in_place_drop; @@ -483,15 +483,13 @@ impl<T> Vec<T> { Self::with_capacity_in(capacity, Global) } - /// Creates a `Vec<T>` directly from the raw components of another vector. + /// 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` needs to have been previously allocated via [`String`]/`Vec<T>` - /// (at least, it's highly likely to be incorrect if it wasn't). /// * `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 @@ -500,6 +498,14 @@ impl<T> Vec<T> { /// 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 @@ -551,6 +557,32 @@ impl<T> Vec<T> { /// 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 { @@ -641,21 +673,30 @@ impl<T, A: Allocator> Vec<T, A> { Vec { buf: RawVec::with_capacity_in(capacity, alloc), len: 0 } } - /// Creates a `Vec<T, A>` directly from the raw components of another vector. + /// 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` needs to have been previously allocated via [`String`]/`Vec<T>` - /// (at least, it's highly likely to be incorrect if it wasn't). - /// * `T` needs to have the same size and alignment as what `ptr` was allocated with. + /// * `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`. - /// * `capacity` needs to be the capacity that the pointer was allocated with. + /// * 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 @@ -673,6 +714,7 @@ impl<T, A: Allocator> Vec<T, A> { /// /// [`String`]: crate::string::String /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc + /// [*fit*]: crate::alloc::Allocator#memory-fitting /// /// # Examples /// @@ -711,6 +753,29 @@ impl<T, A: Allocator> Vec<T, A> { /// 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 { @@ -803,13 +868,14 @@ impl<T, A: Allocator> Vec<T, A> { (ptr, len, capacity, alloc) } - /// Returns the number of elements the vector can hold without + /// Returns the total number of elements the vector can hold without /// reallocating. /// /// # Examples /// /// ``` - /// let vec: Vec<i32> = Vec::with_capacity(10); + /// let mut vec: Vec<i32> = Vec::with_capacity(10); + /// vec.push(42); /// assert_eq!(vec.capacity(), 10); /// ``` #[inline] @@ -1774,6 +1840,51 @@ impl<T, A: Allocator> Vec<T, A> { } } + /// 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. /// @@ -1889,9 +2000,7 @@ impl<T, A: Allocator> Vec<T, A> { unsafe { // set self.vec length's to start, to be safe in case Drain is leaked self.set_len(start); - // Use the borrow in the IterMut to indicate borrowing behavior of the - // whole Drain iterator (like &mut T). - let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(start), end - start); + let range_slice = slice::from_raw_parts(self.as_ptr().add(start), end - start); Drain { tail_start: end, tail_len: len - end, @@ -2083,7 +2192,6 @@ impl<T, A: Allocator> Vec<T, A> { /// static_ref[0] += 1; /// assert_eq!(static_ref, &[2, 2, 3]); /// ``` - #[cfg(not(no_global_oom_handling))] #[stable(feature = "vec_leak", since = "1.47.0")] #[inline] pub fn leak<'a>(self) -> &'a mut [T] @@ -2347,7 +2455,7 @@ impl<T, A: Allocator, const N: usize> Vec<[T; N], A> { #[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 mem::size_of::<T>() == 0 { + let (new_len, new_cap) = if T::IS_ZST { (len.checked_mul(N).expect("vec len overflow"), usize::MAX) } else { // SAFETY: @@ -2677,7 +2785,7 @@ impl<T, A: Allocator> IntoIterator for Vec<T, A> { let mut me = ManuallyDrop::new(self); let alloc = ManuallyDrop::new(ptr::read(me.allocator())); let begin = me.as_mut_ptr(); - let end = if mem::size_of::<T>() == 0 { + let end = if T::IS_ZST { begin.wrapping_byte_add(me.len()) } else { begin.add(me.len()) as *const T |