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| -rw-r--r-- | rust/alloc/boxed.rs | 2429 |
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diff --git a/rust/alloc/boxed.rs b/rust/alloc/boxed.rs new file mode 100644 index 0000000000..c8173cea83 --- /dev/null +++ b/rust/alloc/boxed.rs @@ -0,0 +1,2429 @@ +// SPDX-License-Identifier: Apache-2.0 OR MIT + +//! The `Box<T>` type for heap allocation. +//! +//! [`Box<T>`], casually referred to as a 'box', provides the simplest form of +//! heap allocation in Rust. Boxes provide ownership for this allocation, and +//! drop their contents when they go out of scope. Boxes also ensure that they +//! never allocate more than `isize::MAX` bytes. +//! +//! # Examples +//! +//! Move a value from the stack to the heap by creating a [`Box`]: +//! +//! ``` +//! let val: u8 = 5; +//! let boxed: Box<u8> = Box::new(val); +//! ``` +//! +//! Move a value from a [`Box`] back to the stack by [dereferencing]: +//! +//! ``` +//! let boxed: Box<u8> = Box::new(5); +//! let val: u8 = *boxed; +//! ``` +//! +//! Creating a recursive data structure: +//! +//! ``` +//! #[derive(Debug)] +//! enum List<T> { +//! Cons(T, Box<List<T>>), +//! Nil, +//! } +//! +//! let list: List<i32> = List::Cons(1, Box::new(List::Cons(2, Box::new(List::Nil)))); +//! println!("{list:?}"); +//! ``` +//! +//! This will print `Cons(1, Cons(2, Nil))`. +//! +//! Recursive structures must be boxed, because if the definition of `Cons` +//! looked like this: +//! +//! ```compile_fail,E0072 +//! # enum List<T> { +//! Cons(T, List<T>), +//! # } +//! ``` +//! +//! It wouldn't work. This is because the size of a `List` depends on how many +//! elements are in the list, and so we don't know how much memory to allocate +//! for a `Cons`. By introducing a [`Box<T>`], which has a defined size, we know how +//! big `Cons` needs to be. +//! +//! # Memory layout +//! +//! For non-zero-sized values, a [`Box`] will use the [`Global`] allocator for +//! its allocation. It is valid to convert both ways between a [`Box`] and a +//! raw pointer allocated with the [`Global`] allocator, given that the +//! [`Layout`] used with the allocator is correct for the type. More precisely, +//! a `value: *mut T` that has been allocated with the [`Global`] allocator +//! with `Layout::for_value(&*value)` may be converted into a box using +//! [`Box::<T>::from_raw(value)`]. Conversely, the memory backing a `value: *mut +//! T` obtained from [`Box::<T>::into_raw`] may be deallocated using the +//! [`Global`] allocator with [`Layout::for_value(&*value)`]. +//! +//! For zero-sized values, the `Box` pointer still has to be [valid] for reads +//! and writes and sufficiently aligned. In particular, casting any aligned +//! non-zero integer literal to a raw pointer produces a valid pointer, but a +//! pointer pointing into previously allocated memory that since got freed is +//! not valid. The recommended way to build a Box to a ZST if `Box::new` cannot +//! be used is to use [`ptr::NonNull::dangling`]. +//! +//! So long as `T: Sized`, a `Box<T>` is guaranteed to be represented +//! as a single pointer and is also ABI-compatible with C pointers +//! (i.e. the C type `T*`). This means that if you have extern "C" +//! Rust functions that will be called from C, you can define those +//! Rust functions using `Box<T>` types, and use `T*` as corresponding +//! type on the C side. As an example, consider this C header which +//! declares functions that create and destroy some kind of `Foo` +//! value: +//! +//! ```c +//! /* C header */ +//! +//! /* Returns ownership to the caller */ +//! struct Foo* foo_new(void); +//! +//! /* Takes ownership from the caller; no-op when invoked with null */ +//! void foo_delete(struct Foo*); +//! ``` +//! +//! These two functions might be implemented in Rust as follows. Here, the +//! `struct Foo*` type from C is translated to `Box<Foo>`, which captures +//! the ownership constraints. Note also that the nullable argument to +//! `foo_delete` is represented in Rust as `Option<Box<Foo>>`, since `Box<Foo>` +//! cannot be null. +//! +//! ``` +//! #[repr(C)] +//! pub struct Foo; +//! +//! #[no_mangle] +//! pub extern "C" fn foo_new() -> Box<Foo> { +//! Box::new(Foo) +//! } +//! +//! #[no_mangle] +//! pub extern "C" fn foo_delete(_: Option<Box<Foo>>) {} +//! ``` +//! +//! Even though `Box<T>` has the same representation and C ABI as a C pointer, +//! this does not mean that you can convert an arbitrary `T*` into a `Box<T>` +//! and expect things to work. `Box<T>` values will always be fully aligned, +//! non-null pointers. Moreover, the destructor for `Box<T>` will attempt to +//! free the value with the global allocator. In general, the best practice +//! is to only use `Box<T>` for pointers that originated from the global +//! allocator. +//! +//! **Important.** At least at present, you should avoid using +//! `Box<T>` types for functions that are defined in C but invoked +//! from Rust. In those cases, you should directly mirror the C types +//! as closely as possible. Using types like `Box<T>` where the C +//! definition is just using `T*` can lead to undefined behavior, as +//! described in [rust-lang/unsafe-code-guidelines#198][ucg#198]. +//! +//! # Considerations for unsafe code +//! +//! **Warning: This section is not normative and is subject to change, possibly +//! being relaxed in the future! It is a simplified summary of the rules +//! currently implemented in the compiler.** +//! +//! The aliasing rules for `Box<T>` are the same as for `&mut T`. `Box<T>` +//! asserts uniqueness over its content. Using raw pointers derived from a box +//! after that box has been mutated through, moved or borrowed as `&mut T` +//! is not allowed. For more guidance on working with box from unsafe code, see +//! [rust-lang/unsafe-code-guidelines#326][ucg#326]. +//! +//! +//! [ucg#198]: https://github.com/rust-lang/unsafe-code-guidelines/issues/198 +//! [ucg#326]: https://github.com/rust-lang/unsafe-code-guidelines/issues/326 +//! [dereferencing]: core::ops::Deref +//! [`Box::<T>::from_raw(value)`]: Box::from_raw +//! [`Global`]: crate::alloc::Global +//! [`Layout`]: crate::alloc::Layout +//! [`Layout::for_value(&*value)`]: crate::alloc::Layout::for_value +//! [valid]: ptr#safety + +#![stable(feature = "rust1", since = "1.0.0")] + +use core::any::Any; +use core::async_iter::AsyncIterator; +use core::borrow; +use core::cmp::Ordering; +use core::error::Error; +use core::fmt; +use core::future::Future; +use core::hash::{Hash, Hasher}; +use core::iter::FusedIterator; +use core::marker::Tuple; +use core::marker::Unsize; +use core::mem; +use core::ops::{ + CoerceUnsized, Deref, DerefMut, DispatchFromDyn, Generator, GeneratorState, Receiver, +}; +use core::pin::Pin; +use core::ptr::{self, Unique}; +use core::task::{Context, Poll}; + +#[cfg(not(no_global_oom_handling))] +use crate::alloc::{handle_alloc_error, WriteCloneIntoRaw}; +use crate::alloc::{AllocError, Allocator, Global, Layout}; +#[cfg(not(no_global_oom_handling))] +use crate::borrow::Cow; +use crate::raw_vec::RawVec; +#[cfg(not(no_global_oom_handling))] +use crate::str::from_boxed_utf8_unchecked; +#[cfg(not(no_global_oom_handling))] +use crate::string::String; +#[cfg(not(no_global_oom_handling))] +use crate::vec::Vec; + +#[cfg(not(no_thin))] +#[unstable(feature = "thin_box", issue = "92791")] +pub use thin::ThinBox; + +#[cfg(not(no_thin))] +mod thin; + +/// A pointer type that uniquely owns a heap allocation of type `T`. +/// +/// See the [module-level documentation](../../std/boxed/index.html) for more. +#[lang = "owned_box"] +#[fundamental] +#[stable(feature = "rust1", since = "1.0.0")] +// The declaration of the `Box` struct must be kept in sync with the +// `alloc::alloc::box_free` function or ICEs will happen. See the comment +// on `box_free` for more details. +pub struct Box< + T: ?Sized, + #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global, +>(Unique<T>, A); + +impl<T> Box<T> { + /// Allocates memory on the heap and then places `x` into it. + /// + /// This doesn't actually allocate if `T` is zero-sized. + /// + /// # Examples + /// + /// ``` + /// let five = Box::new(5); + /// ``` + #[cfg(all(not(no_global_oom_handling)))] + #[inline(always)] + #[stable(feature = "rust1", since = "1.0.0")] + #[must_use] + #[rustc_diagnostic_item = "box_new"] + pub fn new(x: T) -> Self { + #[rustc_box] + Box::new(x) + } + + /// Constructs a new box with uninitialized contents. + /// + /// # Examples + /// + /// ``` + /// #![feature(new_uninit)] + /// + /// let mut five = Box::<u32>::new_uninit(); + /// + /// let five = unsafe { + /// // Deferred initialization: + /// five.as_mut_ptr().write(5); + /// + /// five.assume_init() + /// }; + /// + /// assert_eq!(*five, 5) + /// ``` + #[cfg(not(no_global_oom_handling))] + #[unstable(feature = "new_uninit", issue = "63291")] + #[must_use] + #[inline] + pub fn new_uninit() -> Box<mem::MaybeUninit<T>> { + Self::new_uninit_in(Global) + } + + /// Constructs a new `Box` with uninitialized contents, with the memory + /// being filled with `0` bytes. + /// + /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage + /// of this method. + /// + /// # Examples + /// + /// ``` + /// #![feature(new_uninit)] + /// + /// let zero = Box::<u32>::new_zeroed(); + /// let zero = unsafe { zero.assume_init() }; + /// + /// assert_eq!(*zero, 0) + /// ``` + /// + /// [zeroed]: mem::MaybeUninit::zeroed + #[cfg(not(no_global_oom_handling))] + #[inline] + #[unstable(feature = "new_uninit", issue = "63291")] + #[must_use] + pub fn new_zeroed() -> Box<mem::MaybeUninit<T>> { + Self::new_zeroed_in(Global) + } + + /// Constructs a new `Pin<Box<T>>`. If `T` does not implement [`Unpin`], then + /// `x` will be pinned in memory and unable to be moved. + /// + /// Constructing and pinning of the `Box` can also be done in two steps: `Box::pin(x)` + /// does the same as <code>[Box::into_pin]\([Box::new]\(x))</code>. Consider using + /// [`into_pin`](Box::into_pin) if you already have a `Box<T>`, or if you want to + /// construct a (pinned) `Box` in a different way than with [`Box::new`]. + #[cfg(not(no_global_oom_handling))] + #[stable(feature = "pin", since = "1.33.0")] + #[must_use] + #[inline(always)] + pub fn pin(x: T) -> Pin<Box<T>> { + Box::new(x).into() + } + + /// Allocates memory on the heap then places `x` into it, + /// returning an error if the allocation fails + /// + /// This doesn't actually allocate if `T` is zero-sized. + /// + /// # Examples + /// + /// ``` + /// #![feature(allocator_api)] + /// + /// let five = Box::try_new(5)?; + /// # Ok::<(), std::alloc::AllocError>(()) + /// ``` + #[unstable(feature = "allocator_api", issue = "32838")] + #[inline] + pub fn try_new(x: T) -> Result<Self, AllocError> { + Self::try_new_in(x, Global) + } + + /// Constructs a new box with uninitialized contents on the heap, + /// returning an error if the allocation fails + /// + /// # Examples + /// + /// ``` + /// #![feature(allocator_api, new_uninit)] + /// + /// let mut five = Box::<u32>::try_new_uninit()?; + /// + /// let five = unsafe { + /// // Deferred initialization: + /// five.as_mut_ptr().write(5); + /// + /// five.assume_init() + /// }; + /// + /// assert_eq!(*five, 5); + /// # Ok::<(), std::alloc::AllocError>(()) + /// ``` + #[unstable(feature = "allocator_api", issue = "32838")] + // #[unstable(feature = "new_uninit", issue = "63291")] + #[inline] + pub fn try_new_uninit() -> Result<Box<mem::MaybeUninit<T>>, AllocError> { + Box::try_new_uninit_in(Global) + } + + /// Constructs a new `Box` with uninitialized contents, with the memory + /// being filled with `0` bytes on the heap + /// + /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage + /// of this method. + /// + /// # Examples + /// + /// ``` + /// #![feature(allocator_api, new_uninit)] + /// + /// let zero = Box::<u32>::try_new_zeroed()?; + /// let zero = unsafe { zero.assume_init() }; + /// + /// assert_eq!(*zero, 0); + /// # Ok::<(), std::alloc::AllocError>(()) + /// ``` + /// + /// [zeroed]: mem::MaybeUninit::zeroed + #[unstable(feature = "allocator_api", issue = "32838")] + // #[unstable(feature = "new_uninit", issue = "63291")] + #[inline] + pub fn try_new_zeroed() -> Result<Box<mem::MaybeUninit<T>>, AllocError> { + Box::try_new_zeroed_in(Global) + } +} + +impl<T, A: Allocator> Box<T, A> { + /// Allocates memory in the given allocator then places `x` into it. + /// + /// This doesn't actually allocate if `T` is zero-sized. + /// + /// # Examples + /// + /// ``` + /// #![feature(allocator_api)] + /// + /// use std::alloc::System; + /// + /// let five = Box::new_in(5, System); + /// ``` + #[cfg(not(no_global_oom_handling))] + #[unstable(feature = "allocator_api", issue = "32838")] + #[must_use] + #[inline] + pub fn new_in(x: T, alloc: A) -> Self + where + A: Allocator, + { + let mut boxed = Self::new_uninit_in(alloc); + unsafe { + boxed.as_mut_ptr().write(x); + boxed.assume_init() + } + } + + /// Allocates memory in the given allocator then places `x` into it, + /// returning an error if the allocation fails + /// + /// This doesn't actually allocate if `T` is zero-sized. + /// + /// # Examples + /// + /// ``` + /// #![feature(allocator_api)] + /// + /// use std::alloc::System; + /// + /// let five = Box::try_new_in(5, System)?; + /// # Ok::<(), std::alloc::AllocError>(()) + /// ``` + #[unstable(feature = "allocator_api", issue = "32838")] + #[inline] + pub fn try_new_in(x: T, alloc: A) -> Result<Self, AllocError> + where + A: Allocator, + { + let mut boxed = Self::try_new_uninit_in(alloc)?; + unsafe { + boxed.as_mut_ptr().write(x); + Ok(boxed.assume_init()) + } + } + + /// Constructs a new box with uninitialized contents in the provided allocator. + /// + /// # Examples + /// + /// ``` + /// #![feature(allocator_api, new_uninit)] + /// + /// use std::alloc::System; + /// + /// let mut five = Box::<u32, _>::new_uninit_in(System); + /// + /// let five = unsafe { + /// // Deferred initialization: + /// five.as_mut_ptr().write(5); + /// + /// five.assume_init() + /// }; + /// + /// assert_eq!(*five, 5) + /// ``` + #[unstable(feature = "allocator_api", issue = "32838")] + #[cfg(not(no_global_oom_handling))] + #[must_use] + // #[unstable(feature = "new_uninit", issue = "63291")] + pub fn new_uninit_in(alloc: A) -> Box<mem::MaybeUninit<T>, A> + where + A: Allocator, + { + let layout = Layout::new::<mem::MaybeUninit<T>>(); + // NOTE: Prefer match over unwrap_or_else since closure sometimes not inlineable. + // That would make code size bigger. + match Box::try_new_uninit_in(alloc) { + Ok(m) => m, + Err(_) => handle_alloc_error(layout), + } + } + + /// Constructs a new box with uninitialized contents in the provided allocator, + /// returning an error if the allocation fails + /// + /// # Examples + /// + /// ``` + /// #![feature(allocator_api, new_uninit)] + /// + /// use std::alloc::System; + /// + /// let mut five = Box::<u32, _>::try_new_uninit_in(System)?; + /// + /// let five = unsafe { + /// // Deferred initialization: + /// five.as_mut_ptr().write(5); + /// + /// five.assume_init() + /// }; + /// + /// assert_eq!(*five, 5); + /// # Ok::<(), std::alloc::AllocError>(()) + /// ``` + #[unstable(feature = "allocator_api", issue = "32838")] + // #[unstable(feature = "new_uninit", issue = "63291")] + pub fn try_new_uninit_in(alloc: A) -> Result<Box<mem::MaybeUninit<T>, A>, AllocError> + where + A: Allocator, + { + let layout = Layout::new::<mem::MaybeUninit<T>>(); + let ptr = alloc.allocate(layout)?.cast(); + unsafe { Ok(Box::from_raw_in(ptr.as_ptr(), alloc)) } + } + + /// Constructs a new `Box` with uninitialized contents, with the memory + /// being filled with `0` bytes in the provided allocator. + /// + /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage + /// of this method. + /// + /// # Examples + /// + /// ``` + /// #![feature(allocator_api, new_uninit)] + /// + /// use std::alloc::System; + /// + /// let zero = Box::<u32, _>::new_zeroed_in(System); + /// let zero = unsafe { zero.assume_init() }; + /// + /// assert_eq!(*zero, 0) + /// ``` + /// + /// [zeroed]: mem::MaybeUninit::zeroed + #[unstable(feature = "allocator_api", issue = "32838")] + #[cfg(not(no_global_oom_handling))] + // #[unstable(feature = "new_uninit", issue = "63291")] + #[must_use] + pub fn new_zeroed_in(alloc: A) -> Box<mem::MaybeUninit<T>, A> + where + A: Allocator, + { + let layout = Layout::new::<mem::MaybeUninit<T>>(); + // NOTE: Prefer match over unwrap_or_else since closure sometimes not inlineable. + // That would make code size bigger. + match Box::try_new_zeroed_in(alloc) { + Ok(m) => m, + Err(_) => handle_alloc_error(layout), + } + } + + /// Constructs a new `Box` with uninitialized contents, with the memory + /// being filled with `0` bytes in the provided allocator, + /// returning an error if the allocation fails, + /// + /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage + /// of this method. + /// + /// # Examples + /// + /// ``` + /// #![feature(allocator_api, new_uninit)] + /// + /// use std::alloc::System; + /// + /// let zero = Box::<u32, _>::try_new_zeroed_in(System)?; + /// let zero = unsafe { zero.assume_init() }; + /// + /// assert_eq!(*zero, 0); + /// # Ok::<(), std::alloc::AllocError>(()) + /// ``` + /// + /// [zeroed]: mem::MaybeUninit::zeroed + #[unstable(feature = "allocator_api", issue = "32838")] + // #[unstable(feature = "new_uninit", issue = "63291")] + pub fn try_new_zeroed_in(alloc: A) -> Result<Box<mem::MaybeUninit<T>, A>, AllocError> + where + A: Allocator, + { + let layout = Layout::new::<mem::MaybeUninit<T>>(); + let ptr = alloc.allocate_zeroed(layout)?.cast(); + unsafe { Ok(Box::from_raw_in(ptr.as_ptr(), alloc)) } + } + + /// Constructs a new `Pin<Box<T, A>>`. If `T` does not implement [`Unpin`], then + /// `x` will be pinned in memory and unable to be moved. + /// + /// Constructing and pinning of the `Box` can also be done in two steps: `Box::pin_in(x, alloc)` + /// does the same as <code>[Box::into_pin]\([Box::new_in]\(x, alloc))</code>. Consider using + /// [`into_pin`](Box::into_pin) if you already have a `Box<T, A>`, or if you want to + /// construct a (pinned) `Box` in a different way than with [`Box::new_in`]. + #[cfg(not(no_global_oom_handling))] + #[unstable(feature = "allocator_api", issue = "32838")] + #[must_use] + #[inline(always)] + pub fn pin_in(x: T, alloc: A) -> Pin<Self> + where + A: 'static + Allocator, + { + Self::into_pin(Self::new_in(x, alloc)) + } + + /// Converts a `Box<T>` into a `Box<[T]>` + /// + /// This conversion does not allocate on the heap and happens in place. + #[unstable(feature = "box_into_boxed_slice", issue = "71582")] + pub fn into_boxed_slice(boxed: Self) -> Box<[T], A> { + let (raw, alloc) = Box::into_raw_with_allocator(boxed); + unsafe { Box::from_raw_in(raw as *mut [T; 1], alloc) } + } + + /// Consumes the `Box`, returning the wrapped value. + /// + /// # Examples + /// + /// ``` + /// #![feature(box_into_inner)] + /// + /// let c = Box::new(5); + /// + /// assert_eq!(Box::into_inner(c), 5); + /// ``` + #[unstable(feature = "box_into_inner", issue = "80437")] + #[inline] + pub fn into_inner(boxed: Self) -> T { + *boxed + } +} + +impl<T> Box<[T]> { + /// Constructs a new boxed slice with uninitialized contents. + /// + /// # Examples + /// + /// ``` + /// #![feature(new_uninit)] + /// + /// let mut values = Box::<[u32]>::new_uninit_slice(3); + /// + /// let values = unsafe { + /// // Deferred initialization: + /// values[0].as_mut_ptr().write(1); + /// values[1].as_mut_ptr().write(2); + /// values[2].as_mut_ptr().write(3); + /// + /// values.assume_init() + /// }; + /// + /// assert_eq!(*values, [1, 2, 3]) + /// ``` + #[cfg(not(no_global_oom_handling))] + #[unstable(feature = "new_uninit", issue = "63291")] + #[must_use] + pub fn new_uninit_slice(len: usize) -> Box<[mem::MaybeUninit<T>]> { + unsafe { RawVec::with_capacity(len).into_box(len) } + } + + /// Constructs a new boxed slice with uninitialized contents, with the memory + /// being filled with `0` bytes. + /// + /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage + /// of this method. + /// + /// # Examples + /// + /// ``` + /// #![feature(new_uninit)] + /// + /// let values = Box::<[u32]>::new_zeroed_slice(3); + /// let values = unsafe { values.assume_init() }; + /// + /// assert_eq!(*values, [0, 0, 0]) + /// ``` + /// + /// [zeroed]: mem::MaybeUninit::zeroed + #[cfg(not(no_global_oom_handling))] + #[unstable(feature = "new_uninit", issue = "63291")] + #[must_use] + pub fn new_zeroed_slice(len: usize) -> Box<[mem::MaybeUninit<T>]> { + unsafe { RawVec::with_capacity_zeroed(len).into_box(len) } + } + + /// Constructs a new boxed slice with uninitialized contents. Returns an error if + /// the allocation fails + /// + /// # Examples + /// + /// ``` + /// #![feature(allocator_api, new_uninit)] + /// + /// let mut values = Box::<[u32]>::try_new_uninit_slice(3)?; + /// let values = unsafe { + /// // Deferred initialization: + /// values[0].as_mut_ptr().write(1); + /// values[1].as_mut_ptr().write(2); + /// values[2].as_mut_ptr().write(3); + /// values.assume_init() + /// }; + /// + /// assert_eq!(*values, [1, 2, 3]); + /// # Ok::<(), std::alloc::AllocError>(()) + /// ``` + #[unstable(feature = "allocator_api", issue = "32838")] + #[inline] + pub fn try_new_uninit_slice(len: usize) -> Result<Box<[mem::MaybeUninit<T>]>, AllocError> { + unsafe { + let layout = match Layout::array::<mem::MaybeUninit<T>>(len) { + Ok(l) => l, + Err(_) => return Err(AllocError), + }; + let ptr = Global.allocate(layout)?; + Ok(RawVec::from_raw_parts_in(ptr.as_mut_ptr() as *mut _, len, Global).into_box(len)) + } + } + + /// Constructs a new boxed slice with uninitialized contents, with the memory + /// being filled with `0` bytes. Returns an error if the allocation fails + /// + /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage + /// of this method. + /// + /// # Examples + /// + /// ``` + /// #![feature(allocator_api, new_uninit)] + /// + /// let values = Box::<[u32]>::try_new_zeroed_slice(3)?; + /// let values = unsafe { values.assume_init() }; + /// + /// assert_eq!(*values, [0, 0, 0]); + /// # Ok::<(), std::alloc::AllocError>(()) + /// ``` + /// + /// [zeroed]: mem::MaybeUninit::zeroed + #[unstable(feature = "allocator_api", issue = "32838")] + #[inline] + pub fn try_new_zeroed_slice(len: usize) -> Result<Box<[mem::MaybeUninit<T>]>, AllocError> { + unsafe { + let layout = match Layout::array::<mem::MaybeUninit<T>>(len) { + Ok(l) => l, + Err(_) => return Err(AllocError), + }; + let ptr = Global.allocate_zeroed(layout)?; + Ok(RawVec::from_raw_parts_in(ptr.as_mut_ptr() as *mut _, len, Global).into_box(len)) + } + } +} + +impl<T, A: Allocator> Box<[T], A> { + /// Constructs a new boxed slice with uninitialized contents in the provided allocator. + /// + /// # Examples + /// + /// ``` + /// #![feature(allocator_api, new_uninit)] + /// + /// use std::alloc::System; + /// + /// let mut values = Box::<[u32], _>::new_uninit_slice_in(3, System); + /// + /// let values = unsafe { + /// // Deferred initialization: + /// values[0].as_mut_ptr().write(1); + /// values[1].as_mut_ptr().write(2); + /// values[2].as_mut_ptr().write(3); + /// + /// values.assume_init() + /// }; + /// + /// assert_eq!(*values, [1, 2, 3]) + /// ``` + #[cfg(not(no_global_oom_handling))] + #[unstable(feature = "allocator_api", issue = "32838")] + // #[unstable(feature = "new_uninit", issue = "63291")] + #[must_use] + pub fn new_uninit_slice_in(len: usize, alloc: A) -> Box<[mem::MaybeUninit<T>], A> { + unsafe { RawVec::with_capacity_in(len, alloc).into_box(len) } + } + + /// Constructs a new boxed slice with uninitialized contents in the provided allocator, + /// with the memory being filled with `0` bytes. + /// + /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage + /// of this method. + /// + /// # Examples + /// + /// ``` + /// #![feature(allocator_api, new_uninit)] + /// + /// use std::alloc::System; + /// + /// let values = Box::<[u32], _>::new_zeroed_slice_in(3, System); + /// let values = unsafe { values.assume_init() }; + /// + /// assert_eq!(*values, [0, 0, 0]) + /// ``` + /// + /// [zeroed]: mem::MaybeUninit::zeroed + #[cfg(not(no_global_oom_handling))] + #[unstable(feature = "allocator_api", issue = "32838")] + // #[unstable(feature = "new_uninit", issue = "63291")] + #[must_use] + pub fn new_zeroed_slice_in(len: usize, alloc: A) -> Box<[mem::MaybeUninit<T>], A> { + unsafe { RawVec::with_capacity_zeroed_in(len, alloc).into_box(len) } + } +} + +impl<T, A: Allocator> Box<mem::MaybeUninit<T>, A> { + /// Converts to `Box<T, A>`. + /// + /// # Safety + /// + /// As with [`MaybeUninit::assume_init`], + /// it is up to the caller to guarantee that the value + /// really is in an initialized state. + /// Calling this when the content is not yet fully initialized + /// causes immediate undefined behavior. + /// + /// [`MaybeUninit::assume_init`]: mem::MaybeUninit::assume_init + /// + /// # Examples + /// + /// ``` + /// #![feature(new_uninit)] + /// + /// let mut five = Box::<u32>::new_uninit(); + /// + /// let five: Box<u32> = unsafe { + /// // Deferred initialization: + /// five.as_mut_ptr().write(5); + /// + /// five.assume_init() + /// }; + /// + /// assert_eq!(*five, 5) + /// ``` + #[unstable(feature = "new_uninit", issue = "63291")] + #[inline] + pub unsafe fn assume_init(self) -> Box<T, A> { + let (raw, alloc) = Box::into_raw_with_allocator(self); + unsafe { Box::from_raw_in(raw as *mut T, alloc) } + } + + /// Writes the value and converts to `Box<T, A>`. + /// + /// This method converts the box similarly to [`Box::assume_init`] but + /// writes `value` into it before conversion thus guaranteeing safety. + /// In some scenarios use of this method may improve performance because + /// the compiler may be able to optimize copying from stack. + /// + /// # Examples + /// + /// ``` + /// #![feature(new_uninit)] + /// + /// let big_box = Box::<[usize; 1024]>::new_uninit(); + /// + /// let mut array = [0; 1024]; + /// for (i, place) in array.iter_mut().enumerate() { + /// *place = i; + /// } + /// + /// // The optimizer may be able to elide this copy, so previous code writes + /// // to heap directly. + /// let big_box = Box::write(big_box, array); + /// + /// for (i, x) in big_box.iter().enumerate() { + /// assert_eq!(*x, i); + /// } + /// ``` + #[unstable(feature = "new_uninit", issue = "63291")] + #[inline] + pub fn write(mut boxed: Self, value: T) -> Box<T, A> { + unsafe { + (*boxed).write(value); + boxed.assume_init() + } + } +} + +impl<T, A: Allocator> Box<[mem::MaybeUninit<T>], A> { + /// Converts to `Box<[T], A>`. + /// + /// # Safety + /// + /// As with [`MaybeUninit::assume_init`], + /// it is up to the caller to guarantee that the values + /// really are in an initialized state. + /// Calling this when the content is not yet fully initialized + /// causes immediate undefined behavior. + /// + /// [`MaybeUninit::assume_init`]: mem::MaybeUninit::assume_init + /// + /// # Examples + /// + /// ``` + /// #![feature(new_uninit)] + /// + /// let mut values = Box::<[u32]>::new_uninit_slice(3); + /// + /// let values = unsafe { + /// // Deferred initialization: + /// values[0].as_mut_ptr().write(1); + /// values[1].as_mut_ptr().write(2); + /// values[2].as_mut_ptr().write(3); + /// + /// values.assume_init() + /// }; + /// + /// assert_eq!(*values, [1, 2, 3]) + /// ``` + #[unstable(feature = "new_uninit", issue = "63291")] + #[inline] + pub unsafe fn assume_init(self) -> Box<[T], A> { + let (raw, alloc) = Box::into_raw_with_allocator(self); + unsafe { Box::from_raw_in(raw as *mut [T], alloc) } + } +} + +impl<T: ?Sized> Box<T> { + /// Constructs a box from a raw pointer. + /// + /// After calling this function, the raw pointer is owned by the + /// resulting `Box`. Specifically, the `Box` destructor will call + /// the destructor of `T` and free the allocated memory. For this + /// to be safe, the memory must have been allocated in accordance + /// with the [memory layout] used by `Box` . + /// + /// # Safety + /// + /// This function is unsafe because improper use may lead to + /// memory problems. For example, a double-free may occur if the + /// function is called twice on the same raw pointer. + /// + /// The safety conditions are described in the [memory layout] section. + /// + /// # Examples + /// + /// Recreate a `Box` which was previously converted to a raw pointer + /// using [`Box::into_raw`]: + /// ``` + /// let x = Box::new(5); + /// let ptr = Box::into_raw(x); + /// let x = unsafe { Box::from_raw(ptr) }; + /// ``` + /// Manually create a `Box` from scratch by using the global allocator: + /// ``` + /// use std::alloc::{alloc, Layout}; + /// + /// unsafe { + /// let ptr = alloc(Layout::new::<i32>()) as *mut i32; + /// // In general .write is required to avoid attempting to destruct + /// // the (uninitialized) previous contents of `ptr`, though for this + /// // simple example `*ptr = 5` would have worked as well. + /// ptr.write(5); + /// let x = Box::from_raw(ptr); + /// } + /// ``` + /// + /// [memory layout]: self#memory-layout + /// [`Layout`]: crate::Layout + #[stable(feature = "box_raw", since = "1.4.0")] + #[inline] + #[must_use = "call `drop(Box::from_raw(ptr))` if you intend to drop the `Box`"] + pub unsafe fn from_raw(raw: *mut T) -> Self { + unsafe { Self::from_raw_in(raw, Global) } + } +} + +impl<T: ?Sized, A: Allocator> Box<T, A> { + /// Constructs a box from a raw pointer in the given allocator. + /// + /// After calling this function, the raw pointer is owned by the + /// resulting `Box`. Specifically, the `Box` destructor will call + /// the destructor of `T` and free the allocated memory. For this + /// to be safe, the memory must have been allocated in accordance + /// with the [memory layout] used by `Box` . + /// + /// # Safety + /// + /// This function is unsafe because improper use may lead to + /// memory problems. For example, a double-free may occur if the + /// function is called twice on the same raw pointer. + /// + /// + /// # Examples + /// + /// Recreate a `Box` which was previously converted to a raw pointer + /// using [`Box::into_raw_with_allocator`]: + /// ``` + /// #![feature(allocator_api)] + /// + /// use std::alloc::System; + /// + /// let x = Box::new_in(5, System); + /// let (ptr, alloc) = Box::into_raw_with_allocator(x); + /// let x = unsafe { Box::from_raw_in(ptr, alloc) }; + /// ``` + /// Manually create a `Box` from scratch by using the system allocator: + /// ``` + /// #![feature(allocator_api, slice_ptr_get)] + /// + /// use std::alloc::{Allocator, Layout, System}; + /// + /// unsafe { + /// let ptr = System.allocate(Layout::new::<i32>())?.as_mut_ptr() as *mut i32; + /// // In general .write is required to avoid attempting to destruct + /// // the (uninitialized) previous contents of `ptr`, though for this + /// // simple example `*ptr = 5` would have worked as well. + /// ptr.write(5); + /// let x = Box::from_raw_in(ptr, System); + /// } + /// # Ok::<(), std::alloc::AllocError>(()) + /// ``` + /// + /// [memory layout]: self#memory-layout + /// [`Layout`]: crate::Layout + #[unstable(feature = "allocator_api", issue = "32838")] + #[rustc_const_unstable(feature = "const_box", issue = "92521")] + #[inline] + pub const unsafe fn from_raw_in(raw: *mut T, alloc: A) -> Self { + Box(unsafe { Unique::new_unchecked(raw) }, alloc) + } + + /// Consumes the `Box`, returning a wrapped raw pointer. + /// + /// The pointer will be properly aligned and non-null. + /// + /// After calling this function, the caller is responsible for the + /// memory previously managed by the `Box`. In particular, the + /// caller should properly destroy `T` and release the memory, taking + /// into account the [memory layout] used by `Box`. The easiest way to + /// do this is to convert the raw pointer back into a `Box` with the + /// [`Box::from_raw`] function, allowing the `Box` destructor to perform + /// the cleanup. + /// + /// Note: this is an associated function, which means that you have + /// to call it as `Box::into_raw(b)` instead of `b.into_raw()`. This + /// is so that there is no conflict with a method on the inner type. + /// + /// # Examples + /// Converting the raw pointer back into a `Box` with [`Box::from_raw`] + /// for automatic cleanup: + /// ``` + /// let x = Box::new(String::from("Hello")); + /// let ptr = Box::into_raw(x); + /// let x = unsafe { Box::from_raw(ptr) }; + /// ``` + /// Manual cleanup by explicitly running the destructor and deallocating + /// the memory: + /// ``` + /// use std::alloc::{dealloc, Layout}; + /// use std::ptr; + /// + /// let x = Box::new(String::from("Hello")); + /// let p = Box::into_raw(x); + /// unsafe { + /// ptr::drop_in_place(p); + /// dealloc(p as *mut u8, Layout::new::<String>()); + /// } + /// ``` + /// + /// [memory layout]: self#memory-layout + #[stable(feature = "box_raw", since = "1.4.0")] + #[inline] + pub fn into_raw(b: Self) -> *mut T { + Self::into_raw_with_allocator(b).0 + } + + /// Consumes the `Box`, returning a wrapped raw pointer and the allocator. + /// + /// The pointer will be properly aligned and non-null. + /// + /// After calling this function, the caller is responsible for the + /// memory previously managed by the `Box`. In particular, the + /// caller should properly destroy `T` and release the memory, taking + /// into account the [memory layout] used by `Box`. The easiest way to + /// do this is to convert the raw pointer back into a `Box` with the + /// [`Box::from_raw_in`] function, allowing the `Box` destructor to perform + /// the cleanup. + /// + /// Note: this is an associated function, which means that you have + /// to call it as `Box::into_raw_with_allocator(b)` instead of `b.into_raw_with_allocator()`. This + /// is so that there is no conflict with a method on the inner type. + /// + /// # Examples + /// Converting the raw pointer back into a `Box` with [`Box::from_raw_in`] + /// for automatic cleanup: + /// ``` + /// #![feature(allocator_api)] + /// + /// use std::alloc::System; + /// + /// let x = Box::new_in(String::from("Hello"), System); + /// let (ptr, alloc) = Box::into_raw_with_allocator(x); + /// let x = unsafe { Box::from_raw_in(ptr, alloc) }; + /// ``` + /// Manual cleanup by explicitly running the destructor and deallocating + /// the memory: + /// ``` + /// #![feature(allocator_api)] + /// + /// use std::alloc::{Allocator, Layout, System}; + /// use std::ptr::{self, NonNull}; + /// + /// let x = Box::new_in(String::from("Hello"), System); + /// let (ptr, alloc) = Box::into_raw_with_allocator(x); + /// unsafe { + /// ptr::drop_in_place(ptr); + /// let non_null = NonNull::new_unchecked(ptr); + /// alloc.deallocate(non_null.cast(), Layout::new::<String>()); + /// } + /// ``` + /// + /// [memory layout]: self#memory-layout + #[unstable(feature = "allocator_api", issue = "32838")] + #[inline] + pub fn into_raw_with_allocator(b: Self) -> (*mut T, A) { + let (leaked, alloc) = Box::into_unique(b); + (leaked.as_ptr(), alloc) + } + + #[unstable( + feature = "ptr_internals", + issue = "none", + reason = "use `Box::leak(b).into()` or `Unique::from(Box::leak(b))` instead" + )] + #[inline] + #[doc(hidden)] + pub fn into_unique(b: Self) -> (Unique<T>, A) { + // Box is recognized as a "unique pointer" by Stacked Borrows, but internally it is a + // raw pointer for the type system. Turning it directly into a raw pointer would not be + // recognized as "releasing" the unique pointer to permit aliased raw accesses, + // so all raw pointer methods have to go through `Box::leak`. Turning *that* to a raw pointer + // behaves correctly. + let alloc = unsafe { ptr::read(&b.1) }; + (Unique::from(Box::leak(b)), alloc) + } + + /// Returns a reference to the underlying allocator. + /// + /// Note: this is an associated function, which means that you have + /// to call it as `Box::allocator(&b)` instead of `b.allocator()`. This + /// is so that there is no conflict with a method on the inner type. + #[unstable(feature = "allocator_api", issue = "32838")] + #[rustc_const_unstable(feature = "const_box", issue = "92521")] + #[inline] + pub const fn allocator(b: &Self) -> &A { + &b.1 + } + + /// Consumes and leaks the `Box`, returning a mutable reference, + /// `&'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`. + /// + /// 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. If this is not acceptable, the reference should first be wrapped + /// with the [`Box::from_raw`] function producing a `Box`. This `Box` can + /// then be dropped which will properly destroy `T` and release the + /// allocated memory. + /// + /// Note: this is an associated function, which means that you have + /// to call it as `Box::leak(b)` instead of `b.leak()`. This + /// is so that there is no conflict with a method on the inner type. + /// + /// # Examples + /// + /// Simple usage: + /// + /// ``` + /// let x = Box::new(41); + /// let static_ref: &'static mut usize = Box::leak(x); + /// *static_ref += 1; + /// assert_eq!(*static_ref, 42); + /// ``` + /// + /// Unsized data: + /// + /// ``` + /// let x = vec![1, 2, 3].into_boxed_slice(); + /// let static_ref = Box::leak(x); + /// static_ref[0] = 4; + /// assert_eq!(*static_ref, [4, 2, 3]); + /// ``` + #[stable(feature = "box_leak", since = "1.26.0")] + #[inline] + pub fn leak<'a>(b: Self) -> &'a mut T + where + A: 'a, + { + unsafe { &mut *mem::ManuallyDrop::new(b).0.as_ptr() } + } + + /// Converts a `Box<T>` into a `Pin<Box<T>>`. If `T` does not implement [`Unpin`], then + /// `*boxed` will be pinned in memory and unable to be moved. + /// + /// This conversion does not allocate on the heap and happens in place. + /// + /// This is also available via [`From`]. + /// + /// Constructing and pinning a `Box` with <code>Box::into_pin([Box::new]\(x))</code> + /// can also be written more concisely using <code>[Box::pin]\(x)</code>. + /// This `into_pin` method is useful if you already have a `Box<T>`, or you are + /// constructing a (pinned) `Box` in a different way than with [`Box::new`]. + /// + /// # Notes + /// + /// It's not recommended that crates add an impl like `From<Box<T>> for Pin<T>`, + /// as it'll introduce an ambiguity when calling `Pin::from`. + /// A demonstration of such a poor impl is shown below. + /// + /// ```compile_fail + /// # use std::pin::Pin; + /// struct Foo; // A type defined in this crate. + /// impl From<Box<()>> for Pin<Foo> { + /// fn from(_: Box<()>) -> Pin<Foo> { + /// Pin::new(Foo) + /// } + /// } + /// + /// let foo = Box::new(()); + /// let bar = Pin::from(foo); + /// ``` + #[stable(feature = "box_into_pin", since = "1.63.0")] + #[rustc_const_unstable(feature = "const_box", issue = "92521")] + pub const fn into_pin(boxed: Self) -> Pin<Self> + where + A: 'static, + { + // It's not possible to move or replace the insides of a `Pin<Box<T>>` + // when `T: !Unpin`, so it's safe to pin it directly without any + // additional requirements. + unsafe { Pin::new_unchecked(boxed) } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +unsafe impl<#[may_dangle] T: ?Sized, A: Allocator> Drop for Box<T, A> { + fn drop(&mut self) { + // FIXME: Do nothing, drop is currently performed by compiler. + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Default> Default for Box<T> { + /// Creates a `Box<T>`, with the `Default` value for T. + #[inline] + fn default() -> Self { + Box::new(T::default()) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> Default for Box<[T]> { + #[inline] + fn default() -> Self { + let ptr: Unique<[T]> = Unique::<[T; 0]>::dangling(); + Box(ptr, Global) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "default_box_extra", since = "1.17.0")] +impl Default for Box<str> { + #[inline] + fn default() -> Self { + // SAFETY: This is the same as `Unique::cast<U>` but with an unsized `U = str`. + let ptr: Unique<str> = unsafe { + let bytes: Unique<[u8]> = Unique::<[u8; 0]>::dangling(); + Unique::new_unchecked(bytes.as_ptr() as *mut str) + }; + Box(ptr, Global) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Clone, A: Allocator + Clone> Clone for Box<T, A> { + /// Returns a new box with a `clone()` of this box's contents. + /// + /// # Examples + /// + /// ``` + /// let x = Box::new(5); + /// let y = x.clone(); + /// + /// // The value is the same + /// assert_eq!(x, y); + /// + /// // But they are unique objects + /// assert_ne!(&*x as *const i32, &*y as *const i32); + /// ``` + #[inline] + fn clone(&self) -> Self { + // Pre-allocate memory to allow writing the cloned value directly. + let mut boxed = Self::new_uninit_in(self.1.clone()); + unsafe { + (**self).write_clone_into_raw(boxed.as_mut_ptr()); + boxed.assume_init() + } + } + + /// Copies `source`'s contents into `self` without creating a new allocation. + /// + /// # Examples + /// + /// ``` + /// let x = Box::new(5); + /// let mut y = Box::new(10); + /// let yp: *const i32 = &*y; + /// + /// y.clone_from(&x); + /// + /// // The value is the same + /// assert_eq!(x, y); + /// + /// // And no allocation occurred + /// assert_eq!(yp, &*y); + /// ``` + #[inline] + fn clone_from(&mut self, source: &Self) { + (**self).clone_from(&(**source)); + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "box_slice_clone", since = "1.3.0")] +impl Clone for Box<str> { + fn clone(&self) -> Self { + // this makes a copy of the data + let buf: Box<[u8]> = self.as_bytes().into(); + unsafe { from_boxed_utf8_unchecked(buf) } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: ?Sized + PartialEq, A: Allocator> PartialEq for Box<T, A> { + #[inline] + fn eq(&self, other: &Self) -> bool { + PartialEq::eq(&**self, &**other) + } + #[inline] + fn ne(&self, other: &Self) -> bool { + PartialEq::ne(&**self, &**other) + } +} +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: ?Sized + PartialOrd, A: Allocator> PartialOrd for Box<T, A> { + #[inline] + fn partial_cmp(&self, other: &Self) -> Option<Ordering> { + PartialOrd::partial_cmp(&**self, &**other) + } + #[inline] + fn lt(&self, other: &Self) -> bool { + PartialOrd::lt(&**self, &**other) + } + #[inline] + fn le(&self, other: &Self) -> bool { + PartialOrd::le(&**self, &**other) + } + #[inline] + fn ge(&self, other: &Self) -> bool { + PartialOrd::ge(&**self, &**other) + } + #[inline] + fn gt(&self, other: &Self) -> bool { + PartialOrd::gt(&**self, &**other) + } +} +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: ?Sized + Ord, A: Allocator> Ord for Box<T, A> { + #[inline] + fn cmp(&self, other: &Self) -> Ordering { + Ord::cmp(&**self, &**other) + } +} +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: ?Sized + Eq, A: Allocator> Eq for Box<T, A> {} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: ?Sized + Hash, A: Allocator> Hash for Box<T, A> { + fn hash<H: Hasher>(&self, state: &mut H) { + (**self).hash(state); + } +} + +#[stable(feature = "indirect_hasher_impl", since = "1.22.0")] +impl<T: ?Sized + Hasher, A: Allocator> Hasher for Box<T, A> { + fn finish(&self) -> u64 { + (**self).finish() + } + fn write(&mut self, bytes: &[u8]) { + (**self).write(bytes) + } + fn write_u8(&mut self, i: u8) { + (**self).write_u8(i) + } + fn write_u16(&mut self, i: u16) { + (**self).write_u16(i) + } + fn write_u32(&mut self, i: u32) { + (**self).write_u32(i) + } + fn write_u64(&mut self, i: u64) { + (**self).write_u64(i) + } + fn write_u128(&mut self, i: u128) { + (**self).write_u128(i) + } + fn write_usize(&mut self, i: usize) { + (**self).write_usize(i) + } + fn write_i8(&mut self, i: i8) { + (**self).write_i8(i) + } + fn write_i16(&mut self, i: i16) { + (**self).write_i16(i) + } + fn write_i32(&mut self, i: i32) { + (**self).write_i32(i) + } + fn write_i64(&mut self, i: i64) { + (**self).write_i64(i) + } + fn write_i128(&mut self, i: i128) { + (**self).write_i128(i) + } + fn write_isize(&mut self, i: isize) { + (**self).write_isize(i) + } + fn write_length_prefix(&mut self, len: usize) { + (**self).write_length_prefix(len) + } + fn write_str(&mut self, s: &str) { + (**self).write_str(s) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "from_for_ptrs", since = "1.6.0")] +impl<T> From<T> for Box<T> { + /// Converts a `T` into a `Box<T>` + /// + /// The conversion allocates on the heap and moves `t` + /// from the stack into it. + /// + /// # Examples + /// + /// ```rust + /// let x = 5; + /// let boxed = Box::new(5); + /// + /// assert_eq!(Box::from(x), boxed); + /// ``` + fn from(t: T) -> Self { + Box::new(t) + } +} + +#[stable(feature = "pin", since = "1.33.0")] +impl<T: ?Sized, A: Allocator> From<Box<T, A>> for Pin<Box<T, A>> +where + A: 'static, +{ + /// Converts a `Box<T>` into a `Pin<Box<T>>`. If `T` does not implement [`Unpin`], then + /// `*boxed` will be pinned in memory and unable to be moved. + /// + /// This conversion does not allocate on the heap and happens in place. + /// + /// This is also available via [`Box::into_pin`]. + /// + /// Constructing and pinning a `Box` with <code><Pin<Box\<T>>>::from([Box::new]\(x))</code> + /// can also be written more concisely using <code>[Box::pin]\(x)</code>. + /// This `From` implementation is useful if you already have a `Box<T>`, or you are + /// constructing a (pinned) `Box` in a different way than with [`Box::new`]. + fn from(boxed: Box<T, A>) -> Self { + Box::into_pin(boxed) + } +} + +/// Specialization trait used for `From<&[T]>`. +#[cfg(not(no_global_oom_handling))] +trait BoxFromSlice<T> { + fn from_slice(slice: &[T]) -> Self; +} + +#[cfg(not(no_global_oom_handling))] +impl<T: Clone> BoxFromSlice<T> for Box<[T]> { + #[inline] + default fn from_slice(slice: &[T]) -> Self { + slice.to_vec().into_boxed_slice() + } +} + +#[cfg(not(no_global_oom_handling))] +impl<T: Copy> BoxFromSlice<T> for Box<[T]> { + #[inline] + fn from_slice(slice: &[T]) -> Self { + let len = slice.len(); + let buf = RawVec::with_capacity(len); + unsafe { + ptr::copy_nonoverlapping(slice.as_ptr(), buf.ptr(), len); + buf.into_box(slice.len()).assume_init() + } + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "box_from_slice", since = "1.17.0")] +impl<T: Clone> From<&[T]> for Box<[T]> { + /// Converts a `&[T]` into a `Box<[T]>` + /// + /// This conversion allocates on the heap + /// and performs a copy of `slice` and its contents. + /// + /// # Examples + /// ```rust + /// // create a &[u8] which will be used to create a Box<[u8]> + /// let slice: &[u8] = &[104, 101, 108, 108, 111]; + /// let boxed_slice: Box<[u8]> = Box::from(slice); + /// + /// println!("{boxed_slice:?}"); + /// ``` + #[inline] + fn from(slice: &[T]) -> Box<[T]> { + <Self as BoxFromSlice<T>>::from_slice(slice) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "box_from_cow", since = "1.45.0")] +impl<T: Clone> From<Cow<'_, [T]>> for Box<[T]> { + /// Converts a `Cow<'_, [T]>` into a `Box<[T]>` + /// + /// When `cow` is the `Cow::Borrowed` variant, this + /// conversion allocates on the heap and copies the + /// underlying slice. Otherwise, it will try to reuse the owned + /// `Vec`'s allocation. + #[inline] + fn from(cow: Cow<'_, [T]>) -> Box<[T]> { + match cow { + Cow::Borrowed(slice) => Box::from(slice), + Cow::Owned(slice) => Box::from(slice), + } + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "box_from_slice", since = "1.17.0")] +impl From<&str> for Box<str> { + /// Converts a `&str` into a `Box<str>` + /// + /// This conversion allocates on the heap + /// and performs a copy of `s`. + /// + /// # Examples + /// + /// ```rust + /// let boxed: Box<str> = Box::from("hello"); + /// println!("{boxed}"); + /// ``` + #[inline] + fn from(s: &str) -> Box<str> { + unsafe { from_boxed_utf8_unchecked(Box::from(s.as_bytes())) } + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "box_from_cow", since = "1.45.0")] +impl From<Cow<'_, str>> for Box<str> { + /// Converts a `Cow<'_, str>` into a `Box<str>` + /// + /// When `cow` is the `Cow::Borrowed` variant, this + /// conversion allocates on the heap and copies the + /// underlying `str`. Otherwise, it will try to reuse the owned + /// `String`'s allocation. + /// + /// # Examples + /// + /// ```rust + /// use std::borrow::Cow; + /// + /// let unboxed = Cow::Borrowed("hello"); + /// let boxed: Box<str> = Box::from(unboxed); + /// println!("{boxed}"); + /// ``` + /// + /// ```rust + /// # use std::borrow::Cow; + /// let unboxed = Cow::Owned("hello".to_string()); + /// let boxed: Box<str> = Box::from(unboxed); + /// println!("{boxed}"); + /// ``` + #[inline] + fn from(cow: Cow<'_, str>) -> Box<str> { + match cow { + Cow::Borrowed(s) => Box::from(s), + Cow::Owned(s) => Box::from(s), + } + } +} + +#[stable(feature = "boxed_str_conv", since = "1.19.0")] +impl<A: Allocator> From<Box<str, A>> for Box<[u8], A> { + /// Converts a `Box<str>` into a `Box<[u8]>` + /// + /// This conversion does not allocate on the heap and happens in place. + /// + /// # Examples + /// ```rust + /// // create a Box<str> which will be used to create a Box<[u8]> + /// let boxed: Box<str> = Box::from("hello"); + /// let boxed_str: Box<[u8]> = Box::from(boxed); + /// + /// // create a &[u8] which will be used to create a Box<[u8]> + /// let slice: &[u8] = &[104, 101, 108, 108, 111]; + /// let boxed_slice = Box::from(slice); + /// + /// assert_eq!(boxed_slice, boxed_str); + /// ``` + #[inline] + fn from(s: Box<str, A>) -> Self { + let (raw, alloc) = Box::into_raw_with_allocator(s); + unsafe { Box::from_raw_in(raw as *mut [u8], alloc) } + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "box_from_array", since = "1.45.0")] +impl<T, const N: usize> From<[T; N]> for Box<[T]> { + /// Converts a `[T; N]` into a `Box<[T]>` + /// + /// This conversion moves the array to newly heap-allocated memory. + /// + /// # Examples + /// + /// ```rust + /// let boxed: Box<[u8]> = Box::from([4, 2]); + /// println!("{boxed:?}"); + /// ``` + fn from(array: [T; N]) -> Box<[T]> { + Box::new(array) + } +} + +/// Casts a boxed slice to a boxed array. +/// +/// # Safety +/// +/// `boxed_slice.len()` must be exactly `N`. +unsafe fn boxed_slice_as_array_unchecked<T, A: Allocator, const N: usize>( + boxed_slice: Box<[T], A>, +) -> Box<[T; N], A> { + debug_assert_eq!(boxed_slice.len(), N); + + let (ptr, alloc) = Box::into_raw_with_allocator(boxed_slice); + // SAFETY: Pointer and allocator came from an existing box, + // and our safety condition requires that the length is exactly `N` + unsafe { Box::from_raw_in(ptr as *mut [T; N], alloc) } +} + +#[stable(feature = "boxed_slice_try_from", since = "1.43.0")] +impl<T, const N: usize> TryFrom<Box<[T]>> for Box<[T; N]> { + type Error = Box<[T]>; + + /// Attempts to convert a `Box<[T]>` into a `Box<[T; N]>`. + /// + /// The conversion occurs in-place and does not require a + /// new memory allocation. + /// + /// # Errors + /// + /// Returns the old `Box<[T]>` in the `Err` variant if + /// `boxed_slice.len()` does not equal `N`. + fn try_from(boxed_slice: Box<[T]>) -> Result<Self, Self::Error> { + if boxed_slice.len() == N { + Ok(unsafe { boxed_slice_as_array_unchecked(boxed_slice) }) + } else { + Err(boxed_slice) + } + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "boxed_array_try_from_vec", since = "1.66.0")] +impl<T, const N: usize> TryFrom<Vec<T>> for Box<[T; N]> { + type Error = Vec<T>; + + /// Attempts to convert a `Vec<T>` into a `Box<[T; N]>`. + /// + /// Like [`Vec::into_boxed_slice`], this is in-place if `vec.capacity() == N`, + /// but will require a reallocation otherwise. + /// + /// # Errors + /// + /// Returns the original `Vec<T>` in the `Err` variant if + /// `boxed_slice.len()` does not equal `N`. + /// + /// # Examples + /// + /// This can be used with [`vec!`] to create an array on the heap: + /// + /// ``` + /// let state: Box<[f32; 100]> = vec![1.0; 100].try_into().unwrap(); + /// assert_eq!(state.len(), 100); + /// ``` + fn try_from(vec: Vec<T>) -> Result<Self, Self::Error> { + if vec.len() == N { + let boxed_slice = vec.into_boxed_slice(); + Ok(unsafe { boxed_slice_as_array_unchecked(boxed_slice) }) + } else { + Err(vec) + } + } +} + +impl<A: Allocator> Box<dyn Any, A> { + /// Attempt to downcast the box to a concrete type. + /// + /// # Examples + /// + /// ``` + /// use std::any::Any; + /// + /// fn print_if_string(value: Box<dyn Any>) { + /// if let Ok(string) = value.downcast::<String>() { + /// println!("String ({}): {}", string.len(), string); + /// } + /// } + /// + /// let my_string = "Hello World".to_string(); + /// print_if_string(Box::new(my_string)); + /// print_if_string(Box::new(0i8)); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn downcast<T: Any>(self) -> Result<Box<T, A>, Self> { + if self.is::<T>() { unsafe { Ok(self.downcast_unchecked::<T>()) } } else { Err(self) } + } + + /// Downcasts the box to a concrete type. + /// + /// For a safe alternative see [`downcast`]. + /// + /// # Examples + /// + /// ``` + /// #![feature(downcast_unchecked)] + /// + /// use std::any::Any; + /// + /// let x: Box<dyn Any> = Box::new(1_usize); + /// + /// unsafe { + /// assert_eq!(*x.downcast_unchecked::<usize>(), 1); + /// } + /// ``` + /// + /// # Safety + /// + /// The contained value must be of type `T`. Calling this method + /// with the incorrect type is *undefined behavior*. + /// + /// [`downcast`]: Self::downcast + #[inline] + #[unstable(feature = "downcast_unchecked", issue = "90850")] + pub unsafe fn downcast_unchecked<T: Any>(self) -> Box<T, A> { + debug_assert!(self.is::<T>()); + unsafe { + let (raw, alloc): (*mut dyn Any, _) = Box::into_raw_with_allocator(self); + Box::from_raw_in(raw as *mut T, alloc) + } + } +} + +impl<A: Allocator> Box<dyn Any + Send, A> { + /// Attempt to downcast the box to a concrete type. + /// + /// # Examples + /// + /// ``` + /// use std::any::Any; + /// + /// fn print_if_string(value: Box<dyn Any + Send>) { + /// if let Ok(string) = value.downcast::<String>() { + /// println!("String ({}): {}", string.len(), string); + /// } + /// } + /// + /// let my_string = "Hello World".to_string(); + /// print_if_string(Box::new(my_string)); + /// print_if_string(Box::new(0i8)); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn downcast<T: Any>(self) -> Result<Box<T, A>, Self> { + if self.is::<T>() { unsafe { Ok(self.downcast_unchecked::<T>()) } } else { Err(self) } + } + + /// Downcasts the box to a concrete type. + /// + /// For a safe alternative see [`downcast`]. + /// + /// # Examples + /// + /// ``` + /// #![feature(downcast_unchecked)] + /// + /// use std::any::Any; + /// + /// let x: Box<dyn Any + Send> = Box::new(1_usize); + /// + /// unsafe { + /// assert_eq!(*x.downcast_unchecked::<usize>(), 1); + /// } + /// ``` + /// + /// # Safety + /// + /// The contained value must be of type `T`. Calling this method + /// with the incorrect type is *undefined behavior*. + /// + /// [`downcast`]: Self::downcast + #[inline] + #[unstable(feature = "downcast_unchecked", issue = "90850")] + pub unsafe fn downcast_unchecked<T: Any>(self) -> Box<T, A> { + debug_assert!(self.is::<T>()); + unsafe { + let (raw, alloc): (*mut (dyn Any + Send), _) = Box::into_raw_with_allocator(self); + Box::from_raw_in(raw as *mut T, alloc) + } + } +} + +impl<A: Allocator> Box<dyn Any + Send + Sync, A> { + /// Attempt to downcast the box to a concrete type. + /// + /// # Examples + /// + /// ``` + /// use std::any::Any; + /// + /// fn print_if_string(value: Box<dyn Any + Send + Sync>) { + /// if let Ok(string) = value.downcast::<String>() { + /// println!("String ({}): {}", string.len(), string); + /// } + /// } + /// + /// let my_string = "Hello World".to_string(); + /// print_if_string(Box::new(my_string)); + /// print_if_string(Box::new(0i8)); + /// ``` + #[inline] + #[stable(feature = "box_send_sync_any_downcast", since = "1.51.0")] + pub fn downcast<T: Any>(self) -> Result<Box<T, A>, Self> { + if self.is::<T>() { unsafe { Ok(self.downcast_unchecked::<T>()) } } else { Err(self) } + } + + /// Downcasts the box to a concrete type. + /// + /// For a safe alternative see [`downcast`]. + /// + /// # Examples + /// + /// ``` + /// #![feature(downcast_unchecked)] + /// + /// use std::any::Any; + /// + /// let x: Box<dyn Any + Send + Sync> = Box::new(1_usize); + /// + /// unsafe { + /// assert_eq!(*x.downcast_unchecked::<usize>(), 1); + /// } + /// ``` + /// + /// # Safety + /// + /// The contained value must be of type `T`. Calling this method + /// with the incorrect type is *undefined behavior*. + /// + /// [`downcast`]: Self::downcast + #[inline] + #[unstable(feature = "downcast_unchecked", issue = "90850")] + pub unsafe fn downcast_unchecked<T: Any>(self) -> Box<T, A> { + debug_assert!(self.is::<T>()); + unsafe { + let (raw, alloc): (*mut (dyn Any + Send + Sync), _) = + Box::into_raw_with_allocator(self); + Box::from_raw_in(raw as *mut T, alloc) + } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: fmt::Display + ?Sized, A: Allocator> fmt::Display for Box<T, A> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + fmt::Display::fmt(&**self, f) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: fmt::Debug + ?Sized, A: Allocator> fmt::Debug for Box<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: ?Sized, A: Allocator> fmt::Pointer for Box<T, A> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + // It's not possible to extract the inner Uniq directly from the Box, + // instead we cast it to a *const which aliases the Unique + let ptr: *const T = &**self; + fmt::Pointer::fmt(&ptr, f) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: ?Sized, A: Allocator> Deref for Box<T, A> { + type Target = T; + + fn deref(&self) -> &T { + &**self + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: ?Sized, A: Allocator> DerefMut for Box<T, A> { + fn deref_mut(&mut self) -> &mut T { + &mut **self + } +} + +#[unstable(feature = "receiver_trait", issue = "none")] +impl<T: ?Sized, A: Allocator> Receiver for Box<T, A> {} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<I: Iterator + ?Sized, A: Allocator> Iterator for Box<I, A> { + type Item = I::Item; + fn next(&mut self) -> Option<I::Item> { + (**self).next() + } + fn size_hint(&self) -> (usize, Option<usize>) { + (**self).size_hint() + } + fn nth(&mut self, n: usize) -> Option<I::Item> { + (**self).nth(n) + } + fn last(self) -> Option<I::Item> { + BoxIter::last(self) + } +} + +trait BoxIter { + type Item; + fn last(self) -> Option<Self::Item>; +} + +impl<I: Iterator + ?Sized, A: Allocator> BoxIter for Box<I, A> { + type Item = I::Item; + default fn last(self) -> Option<I::Item> { + #[inline] + fn some<T>(_: Option<T>, x: T) -> Option<T> { + Some(x) + } + + self.fold(None, some) + } +} + +/// Specialization for sized `I`s that uses `I`s implementation of `last()` +/// instead of the default. +#[stable(feature = "rust1", since = "1.0.0")] +impl<I: Iterator, A: Allocator> BoxIter for Box<I, A> { + fn last(self) -> Option<I::Item> { + (*self).last() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<I: DoubleEndedIterator + ?Sized, A: Allocator> DoubleEndedIterator for Box<I, A> { + fn next_back(&mut self) -> Option<I::Item> { + (**self).next_back() + } + fn nth_back(&mut self, n: usize) -> Option<I::Item> { + (**self).nth_back(n) + } +} +#[stable(feature = "rust1", since = "1.0.0")] +impl<I: ExactSizeIterator + ?Sized, A: Allocator> ExactSizeIterator for Box<I, A> { + fn len(&self) -> usize { + (**self).len() + } + fn is_empty(&self) -> bool { + (**self).is_empty() + } +} + +#[stable(feature = "fused", since = "1.26.0")] +impl<I: FusedIterator + ?Sized, A: Allocator> FusedIterator for Box<I, A> {} + +#[stable(feature = "boxed_closure_impls", since = "1.35.0")] +impl<Args: Tuple, F: FnOnce<Args> + ?Sized, A: Allocator> FnOnce<Args> for Box<F, A> { + type Output = <F as FnOnce<Args>>::Output; + + extern "rust-call" fn call_once(self, args: Args) -> Self::Output { + <F as FnOnce<Args>>::call_once(*self, args) + } +} + +#[stable(feature = "boxed_closure_impls", since = "1.35.0")] +impl<Args: Tuple, F: FnMut<Args> + ?Sized, A: Allocator> FnMut<Args> for Box<F, A> { + extern "rust-call" fn call_mut(&mut self, args: Args) -> Self::Output { + <F as FnMut<Args>>::call_mut(self, args) + } +} + +#[stable(feature = "boxed_closure_impls", since = "1.35.0")] +impl<Args: Tuple, F: Fn<Args> + ?Sized, A: Allocator> Fn<Args> for Box<F, A> { + extern "rust-call" fn call(&self, args: Args) -> Self::Output { + <F as Fn<Args>>::call(self, args) + } +} + +#[unstable(feature = "coerce_unsized", issue = "18598")] +impl<T: ?Sized + Unsize<U>, U: ?Sized, A: Allocator> CoerceUnsized<Box<U, A>> for Box<T, A> {} + +#[unstable(feature = "dispatch_from_dyn", issue = "none")] +impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Box<U>> for Box<T, Global> {} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "boxed_slice_from_iter", since = "1.32.0")] +impl<I> FromIterator<I> for Box<[I]> { + fn from_iter<T: IntoIterator<Item = I>>(iter: T) -> Self { + iter.into_iter().collect::<Vec<_>>().into_boxed_slice() + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "box_slice_clone", since = "1.3.0")] +impl<T: Clone, A: Allocator + Clone> Clone for Box<[T], A> { + fn clone(&self) -> Self { + let alloc = Box::allocator(self).clone(); + self.to_vec_in(alloc).into_boxed_slice() + } + + fn clone_from(&mut self, other: &Self) { + if self.len() == other.len() { + self.clone_from_slice(&other); + } else { + *self = other.clone(); + } + } +} + +#[stable(feature = "box_borrow", since = "1.1.0")] +impl<T: ?Sized, A: Allocator> borrow::Borrow<T> for Box<T, A> { + fn borrow(&self) -> &T { + &**self + } +} + +#[stable(feature = "box_borrow", since = "1.1.0")] +impl<T: ?Sized, A: Allocator> borrow::BorrowMut<T> for Box<T, A> { + fn borrow_mut(&mut self) -> &mut T { + &mut **self + } +} + +#[stable(since = "1.5.0", feature = "smart_ptr_as_ref")] +impl<T: ?Sized, A: Allocator> AsRef<T> for Box<T, A> { + fn as_ref(&self) -> &T { + &**self + } +} + +#[stable(since = "1.5.0", feature = "smart_ptr_as_ref")] +impl<T: ?Sized, A: Allocator> AsMut<T> for Box<T, A> { + fn as_mut(&mut self) -> &mut T { + &mut **self + } +} + +/* Nota bene + * + * We could have chosen not to add this impl, and instead have written a + * function of Pin<Box<T>> to Pin<T>. Such a function would not be sound, + * because Box<T> implements Unpin even when T does not, as a result of + * this impl. + * + * We chose this API instead of the alternative for a few reasons: + * - Logically, it is helpful to understand pinning in regard to the + * memory region being pointed to. For this reason none of the + * standard library pointer types support projecting through a pin + * (Box<T> is the only pointer type in std for which this would be + * safe.) + * - It is in practice very useful to have Box<T> be unconditionally + * Unpin because of trait objects, for which the structural auto + * trait functionality does not apply (e.g., Box<dyn Foo> would + * otherwise not be Unpin). + * + * Another type with the same semantics as Box but only a conditional + * implementation of `Unpin` (where `T: Unpin`) would be valid/safe, and + * could have a method to project a Pin<T> from it. + */ +#[stable(feature = "pin", since = "1.33.0")] +impl<T: ?Sized, A: Allocator> Unpin for Box<T, A> where A: 'static {} + +#[unstable(feature = "generator_trait", issue = "43122")] +impl<G: ?Sized + Generator<R> + Unpin, R, A: Allocator> Generator<R> for Box<G, A> +where + A: 'static, +{ + type Yield = G::Yield; + type Return = G::Return; + + fn resume(mut self: Pin<&mut Self>, arg: R) -> GeneratorState<Self::Yield, Self::Return> { + G::resume(Pin::new(&mut *self), arg) + } +} + +#[unstable(feature = "generator_trait", issue = "43122")] +impl<G: ?Sized + Generator<R>, R, A: Allocator> Generator<R> for Pin<Box<G, A>> +where + A: 'static, +{ + type Yield = G::Yield; + type Return = G::Return; + + fn resume(mut self: Pin<&mut Self>, arg: R) -> GeneratorState<Self::Yield, Self::Return> { + G::resume((*self).as_mut(), arg) + } +} + +#[stable(feature = "futures_api", since = "1.36.0")] +impl<F: ?Sized + Future + Unpin, A: Allocator> Future for Box<F, A> +where + A: 'static, +{ + type Output = F::Output; + + fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { + F::poll(Pin::new(&mut *self), cx) + } +} + +#[unstable(feature = "async_iterator", issue = "79024")] +impl<S: ?Sized + AsyncIterator + Unpin> AsyncIterator for Box<S> { + type Item = S::Item; + + fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> { + Pin::new(&mut **self).poll_next(cx) + } + + fn size_hint(&self) -> (usize, Option<usize>) { + (**self).size_hint() + } +} + +impl dyn Error { + #[inline] + #[stable(feature = "error_downcast", since = "1.3.0")] + #[rustc_allow_incoherent_impl] + /// Attempts to downcast the box to a concrete type. + pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<dyn Error>> { + if self.is::<T>() { + unsafe { + let raw: *mut dyn Error = Box::into_raw(self); + Ok(Box::from_raw(raw as *mut T)) + } + } else { + Err(self) + } + } +} + +impl dyn Error + Send { + #[inline] + #[stable(feature = "error_downcast", since = "1.3.0")] + #[rustc_allow_incoherent_impl] + /// Attempts to downcast the box to a concrete type. + pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<dyn Error + Send>> { + let err: Box<dyn Error> = self; + <dyn Error>::downcast(err).map_err(|s| unsafe { + // Reapply the `Send` marker. + mem::transmute::<Box<dyn Error>, Box<dyn Error + Send>>(s) + }) + } +} + +impl dyn Error + Send + Sync { + #[inline] + #[stable(feature = "error_downcast", since = "1.3.0")] + #[rustc_allow_incoherent_impl] + /// Attempts to downcast the box to a concrete type. + pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<Self>> { + let err: Box<dyn Error> = self; + <dyn Error>::downcast(err).map_err(|s| unsafe { + // Reapply the `Send + Sync` marker. + mem::transmute::<Box<dyn Error>, Box<dyn Error + Send + Sync>>(s) + }) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, E: Error + 'a> From<E> for Box<dyn Error + 'a> { + /// Converts a type of [`Error`] into a box of dyn [`Error`]. + /// + /// # Examples + /// + /// ``` + /// use std::error::Error; + /// use std::fmt; + /// use std::mem; + /// + /// #[derive(Debug)] + /// struct AnError; + /// + /// impl fmt::Display for AnError { + /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + /// write!(f, "An error") + /// } + /// } + /// + /// impl Error for AnError {} + /// + /// let an_error = AnError; + /// assert!(0 == mem::size_of_val(&an_error)); + /// let a_boxed_error = Box::<dyn Error>::from(an_error); + /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error)) + /// ``` + fn from(err: E) -> Box<dyn Error + 'a> { + Box::new(err) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<dyn Error + Send + Sync + 'a> { + /// Converts a type of [`Error`] + [`Send`] + [`Sync`] into a box of + /// dyn [`Error`] + [`Send`] + [`Sync`]. + /// + /// # Examples + /// + /// ``` + /// use std::error::Error; + /// use std::fmt; + /// use std::mem; + /// + /// #[derive(Debug)] + /// struct AnError; + /// + /// impl fmt::Display for AnError { + /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + /// write!(f, "An error") + /// } + /// } + /// + /// impl Error for AnError {} + /// + /// unsafe impl Send for AnError {} + /// + /// unsafe impl Sync for AnError {} + /// + /// let an_error = AnError; + /// assert!(0 == mem::size_of_val(&an_error)); + /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(an_error); + /// assert!( + /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error)) + /// ``` + fn from(err: E) -> Box<dyn Error + Send + Sync + 'a> { + Box::new(err) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "rust1", since = "1.0.0")] +impl From<String> for Box<dyn Error + Send + Sync> { + /// Converts a [`String`] into a box of dyn [`Error`] + [`Send`] + [`Sync`]. + /// + /// # Examples + /// + /// ``` + /// use std::error::Error; + /// use std::mem; + /// + /// let a_string_error = "a string error".to_string(); + /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_string_error); + /// assert!( + /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error)) + /// ``` + #[inline] + fn from(err: String) -> Box<dyn Error + Send + Sync> { + struct StringError(String); + + impl Error for StringError { + #[allow(deprecated)] + fn description(&self) -> &str { + &self.0 + } + } + + impl fmt::Display for StringError { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + fmt::Display::fmt(&self.0, f) + } + } + + // Purposefully skip printing "StringError(..)" + impl fmt::Debug for StringError { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + fmt::Debug::fmt(&self.0, f) + } + } + + Box::new(StringError(err)) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "string_box_error", since = "1.6.0")] +impl From<String> for Box<dyn Error> { + /// Converts a [`String`] into a box of dyn [`Error`]. + /// + /// # Examples + /// + /// ``` + /// use std::error::Error; + /// use std::mem; + /// + /// let a_string_error = "a string error".to_string(); + /// let a_boxed_error = Box::<dyn Error>::from(a_string_error); + /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error)) + /// ``` + fn from(str_err: String) -> Box<dyn Error> { + let err1: Box<dyn Error + Send + Sync> = From::from(str_err); + let err2: Box<dyn Error> = err1; + err2 + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a> From<&str> for Box<dyn Error + Send + Sync + 'a> { + /// Converts a [`str`] into a box of dyn [`Error`] + [`Send`] + [`Sync`]. + /// + /// [`str`]: prim@str + /// + /// # Examples + /// + /// ``` + /// use std::error::Error; + /// use std::mem; + /// + /// let a_str_error = "a str error"; + /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_str_error); + /// assert!( + /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error)) + /// ``` + #[inline] + fn from(err: &str) -> Box<dyn Error + Send + Sync + 'a> { + From::from(String::from(err)) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "string_box_error", since = "1.6.0")] +impl From<&str> for Box<dyn Error> { + /// Converts a [`str`] into a box of dyn [`Error`]. + /// + /// [`str`]: prim@str + /// + /// # Examples + /// + /// ``` + /// use std::error::Error; + /// use std::mem; + /// + /// let a_str_error = "a str error"; + /// let a_boxed_error = Box::<dyn Error>::from(a_str_error); + /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error)) + /// ``` + fn from(err: &str) -> Box<dyn Error> { + From::from(String::from(err)) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "cow_box_error", since = "1.22.0")] +impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Send + Sync + 'a> { + /// Converts a [`Cow`] into a box of dyn [`Error`] + [`Send`] + [`Sync`]. + /// + /// # Examples + /// + /// ``` + /// use std::error::Error; + /// use std::mem; + /// use std::borrow::Cow; + /// + /// let a_cow_str_error = Cow::from("a str error"); + /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_cow_str_error); + /// assert!( + /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error)) + /// ``` + fn from(err: Cow<'b, str>) -> Box<dyn Error + Send + Sync + 'a> { + From::from(String::from(err)) + } +} + +#[cfg(not(no_global_oom_handling))] +#[stable(feature = "cow_box_error", since = "1.22.0")] +impl<'a> From<Cow<'a, str>> for Box<dyn Error> { + /// Converts a [`Cow`] into a box of dyn [`Error`]. + /// + /// # Examples + /// + /// ``` + /// use std::error::Error; + /// use std::mem; + /// use std::borrow::Cow; + /// + /// let a_cow_str_error = Cow::from("a str error"); + /// let a_boxed_error = Box::<dyn Error>::from(a_cow_str_error); + /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error)) + /// ``` + fn from(err: Cow<'a, str>) -> Box<dyn Error> { + From::from(String::from(err)) + } +} + +#[stable(feature = "box_error", since = "1.8.0")] +impl<T: core::error::Error> core::error::Error for Box<T> { + #[allow(deprecated, deprecated_in_future)] + fn description(&self) -> &str { + core::error::Error::description(&**self) + } + + #[allow(deprecated)] + fn cause(&self) -> Option<&dyn core::error::Error> { + core::error::Error::cause(&**self) + } + + fn source(&self) -> Option<&(dyn core::error::Error + 'static)> { + core::error::Error::source(&**self) + } +} |