2132 lines
73 KiB
Rust
2132 lines
73 KiB
Rust
//! The `Box<T>` type for heap allocation.
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//!
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//! [`Box<T>`], casually referred to as a 'box', provides the simplest form of
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//! heap allocation in Rust. Boxes provide ownership for this allocation, and
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//! drop their contents when they go out of scope. Boxes also ensure that they
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//! never allocate more than `isize::MAX` bytes.
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//!
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//! # Examples
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//!
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//! Move a value from the stack to the heap by creating a [`Box`]:
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//!
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//! ```
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//! let val: u8 = 5;
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//! let boxed: Box<u8> = Box::new(val);
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//! ```
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//!
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//! Move a value from a [`Box`] back to the stack by [dereferencing]:
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//!
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//! ```
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//! let boxed: Box<u8> = Box::new(5);
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//! let val: u8 = *boxed;
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//! ```
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//!
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//! Creating a recursive data structure:
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//!
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//! ```
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//! # #[allow(dead_code)]
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//! #[derive(Debug)]
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//! enum List<T> {
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//! Cons(T, Box<List<T>>),
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//! Nil,
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//! }
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//!
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//! let list: List<i32> = List::Cons(1, Box::new(List::Cons(2, Box::new(List::Nil))));
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//! println!("{list:?}");
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//! ```
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//!
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//! This will print `Cons(1, Cons(2, Nil))`.
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//!
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//! Recursive structures must be boxed, because if the definition of `Cons`
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//! looked like this:
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//!
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//! ```compile_fail,E0072
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//! # enum List<T> {
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//! Cons(T, List<T>),
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//! # }
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//! ```
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//!
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//! It wouldn't work. This is because the size of a `List` depends on how many
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//! elements are in the list, and so we don't know how much memory to allocate
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//! for a `Cons`. By introducing a [`Box<T>`], which has a defined size, we know how
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//! big `Cons` needs to be.
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//!
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//! # Memory layout
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//!
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//! For non-zero-sized values, a [`Box`] will use the [`Global`] allocator for its allocation. It is
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//! valid to convert both ways between a [`Box`] and a raw pointer allocated with the [`Global`]
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//! allocator, given that the [`Layout`] used with the allocator is correct for the type and the raw
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//! pointer points to a valid value of the right type. More precisely, a `value: *mut T` that has
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//! been allocated with the [`Global`] allocator with `Layout::for_value(&*value)` may be converted
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//! into a box using [`Box::<T>::from_raw(value)`]. Conversely, the memory backing a `value: *mut T`
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//! obtained from [`Box::<T>::into_raw`] may be deallocated using the [`Global`] allocator with
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//! [`Layout::for_value(&*value)`].
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//!
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//! For zero-sized values, the `Box` pointer has to be non-null and sufficiently aligned. The
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//! recommended way to build a Box to a ZST if `Box::new` cannot be used is to use
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//! [`ptr::NonNull::dangling`].
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//!
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//! On top of these basic layout requirements, a `Box<T>` must point to a valid value of `T`.
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//!
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//! So long as `T: Sized`, a `Box<T>` is guaranteed to be represented
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//! as a single pointer and is also ABI-compatible with C pointers
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//! (i.e. the C type `T*`). This means that if you have extern "C"
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//! Rust functions that will be called from C, you can define those
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//! Rust functions using `Box<T>` types, and use `T*` as corresponding
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//! type on the C side. As an example, consider this C header which
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//! declares functions that create and destroy some kind of `Foo`
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//! value:
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//!
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//! ```c
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//! /* C header */
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//!
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//! /* Returns ownership to the caller */
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//! struct Foo* foo_new(void);
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//!
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//! /* Takes ownership from the caller; no-op when invoked with null */
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//! void foo_delete(struct Foo*);
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//! ```
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//!
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//! These two functions might be implemented in Rust as follows. Here, the
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//! `struct Foo*` type from C is translated to `Box<Foo>`, which captures
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//! the ownership constraints. Note also that the nullable argument to
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//! `foo_delete` is represented in Rust as `Option<Box<Foo>>`, since `Box<Foo>`
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//! cannot be null.
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//!
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//! ```
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//! #[repr(C)]
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//! pub struct Foo;
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//!
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//! #[unsafe(no_mangle)]
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//! pub extern "C" fn foo_new() -> Box<Foo> {
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//! Box::new(Foo)
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//! }
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//!
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//! #[unsafe(no_mangle)]
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//! pub extern "C" fn foo_delete(_: Option<Box<Foo>>) {}
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//! ```
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//!
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//! Even though `Box<T>` has the same representation and C ABI as a C pointer,
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//! this does not mean that you can convert an arbitrary `T*` into a `Box<T>`
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//! and expect things to work. `Box<T>` values will always be fully aligned,
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//! non-null pointers. Moreover, the destructor for `Box<T>` will attempt to
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//! free the value with the global allocator. In general, the best practice
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//! is to only use `Box<T>` for pointers that originated from the global
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//! allocator.
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//!
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//! **Important.** At least at present, you should avoid using
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//! `Box<T>` types for functions that are defined in C but invoked
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//! from Rust. In those cases, you should directly mirror the C types
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//! as closely as possible. Using types like `Box<T>` where the C
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//! definition is just using `T*` can lead to undefined behavior, as
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//! described in [rust-lang/unsafe-code-guidelines#198][ucg#198].
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//!
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//! # Considerations for unsafe code
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//!
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//! **Warning: This section is not normative and is subject to change, possibly
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//! being relaxed in the future! It is a simplified summary of the rules
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//! currently implemented in the compiler.**
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//!
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//! The aliasing rules for `Box<T>` are the same as for `&mut T`. `Box<T>`
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//! asserts uniqueness over its content. Using raw pointers derived from a box
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//! after that box has been mutated through, moved or borrowed as `&mut T`
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//! is not allowed. For more guidance on working with box from unsafe code, see
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//! [rust-lang/unsafe-code-guidelines#326][ucg#326].
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//!
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//! # Editions
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//!
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//! A special case exists for the implementation of `IntoIterator` for arrays on the Rust 2021
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//! edition, as documented [here][array]. Unfortunately, it was later found that a similar
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//! workaround should be added for boxed slices, and this was applied in the 2024 edition.
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//!
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//! Specifically, `IntoIterator` is implemented for `Box<[T]>` on all editions, but specific calls
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//! to `into_iter()` for boxed slices will defer to the slice implementation on editions before
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//! 2024:
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//!
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//! ```rust,edition2021
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//! // Rust 2015, 2018, and 2021:
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//!
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//! # #![allow(boxed_slice_into_iter)] // override our `deny(warnings)`
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//! let boxed_slice: Box<[i32]> = vec![0; 3].into_boxed_slice();
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//!
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//! // This creates a slice iterator, producing references to each value.
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//! for item in boxed_slice.into_iter().enumerate() {
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//! let (i, x): (usize, &i32) = item;
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//! println!("boxed_slice[{i}] = {x}");
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//! }
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//!
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//! // The `boxed_slice_into_iter` lint suggests this change for future compatibility:
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//! for item in boxed_slice.iter().enumerate() {
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//! let (i, x): (usize, &i32) = item;
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//! println!("boxed_slice[{i}] = {x}");
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//! }
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//!
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//! // You can explicitly iterate a boxed slice by value using `IntoIterator::into_iter`
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//! for item in IntoIterator::into_iter(boxed_slice).enumerate() {
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//! let (i, x): (usize, i32) = item;
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//! println!("boxed_slice[{i}] = {x}");
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//! }
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//! ```
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//!
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//! Similar to the array implementation, this may be modified in the future to remove this override,
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//! and it's best to avoid relying on this edition-dependent behavior if you wish to preserve
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//! compatibility with future versions of the compiler.
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//!
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//! [ucg#198]: https://github.com/rust-lang/unsafe-code-guidelines/issues/198
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//! [ucg#326]: https://github.com/rust-lang/unsafe-code-guidelines/issues/326
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//! [dereferencing]: core::ops::Deref
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//! [`Box::<T>::from_raw(value)`]: Box::from_raw
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//! [`Global`]: crate::alloc::Global
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//! [`Layout`]: crate::alloc::Layout
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//! [`Layout::for_value(&*value)`]: crate::alloc::Layout::for_value
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//! [valid]: ptr#safety
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#![stable(feature = "rust1", since = "1.0.0")]
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use core::borrow::{Borrow, BorrowMut};
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#[cfg(not(no_global_oom_handling))]
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use core::clone::CloneToUninit;
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use core::cmp::Ordering;
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use core::error::{self, Error};
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use core::fmt;
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use core::future::Future;
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use core::hash::{Hash, Hasher};
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use core::marker::{PointerLike, Tuple, Unsize};
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use core::mem::{self, SizedTypeProperties};
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use core::ops::{
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AsyncFn, AsyncFnMut, AsyncFnOnce, CoerceUnsized, Coroutine, CoroutineState, Deref, DerefMut,
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DerefPure, DispatchFromDyn, LegacyReceiver,
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};
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use core::pin::{Pin, PinCoerceUnsized};
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use core::ptr::{self, NonNull, Unique};
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use core::task::{Context, Poll};
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#[cfg(not(no_global_oom_handling))]
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use crate::alloc::handle_alloc_error;
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use crate::alloc::{AllocError, Allocator, Global, Layout};
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use crate::raw_vec::RawVec;
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#[cfg(not(no_global_oom_handling))]
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use crate::str::from_boxed_utf8_unchecked;
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/// Conversion related impls for `Box<_>` (`From`, `downcast`, etc)
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mod convert;
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/// Iterator related impls for `Box<_>`.
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mod iter;
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/// [`ThinBox`] implementation.
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mod thin;
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#[unstable(feature = "thin_box", issue = "92791")]
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pub use thin::ThinBox;
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/// A pointer type that uniquely owns a heap allocation of type `T`.
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///
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/// See the [module-level documentation](../../std/boxed/index.html) for more.
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#[lang = "owned_box"]
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#[fundamental]
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#[stable(feature = "rust1", since = "1.0.0")]
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#[rustc_insignificant_dtor]
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#[doc(search_unbox)]
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// The declaration of the `Box` struct must be kept in sync with the
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// compiler or ICEs will happen.
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pub struct Box<
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T: ?Sized,
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#[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
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>(Unique<T>, A);
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/// Constructs a `Box<T>` by calling the `exchange_malloc` lang item and moving the argument into
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/// the newly allocated memory. This is an intrinsic to avoid unnecessary copies.
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///
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/// This is the surface syntax for `box <expr>` expressions.
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#[rustc_intrinsic]
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#[unstable(feature = "liballoc_internals", issue = "none")]
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pub fn box_new<T>(x: T) -> Box<T>;
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impl<T> Box<T> {
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/// Allocates memory on the heap and then places `x` into it.
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///
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/// This doesn't actually allocate if `T` is zero-sized.
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///
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/// # Examples
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///
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/// ```
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/// let five = Box::new(5);
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/// ```
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#[cfg(not(no_global_oom_handling))]
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#[inline(always)]
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#[stable(feature = "rust1", since = "1.0.0")]
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#[must_use]
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#[rustc_diagnostic_item = "box_new"]
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#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
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pub fn new(x: T) -> Self {
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return box_new(x);
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}
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/// Constructs a new box with uninitialized contents.
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///
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/// # Examples
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///
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/// ```
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/// let mut five = Box::<u32>::new_uninit();
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/// // Deferred initialization:
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/// five.write(5);
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/// let five = unsafe { five.assume_init() };
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///
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/// assert_eq!(*five, 5)
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/// ```
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#[cfg(not(no_global_oom_handling))]
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#[stable(feature = "new_uninit", since = "1.82.0")]
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#[must_use]
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#[inline]
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pub fn new_uninit() -> Box<mem::MaybeUninit<T>> {
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Self::new_uninit_in(Global)
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}
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/// Constructs a new `Box` with uninitialized contents, with the memory
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/// being filled with `0` bytes.
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///
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/// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage
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/// of this method.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(new_zeroed_alloc)]
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///
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/// let zero = Box::<u32>::new_zeroed();
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/// let zero = unsafe { zero.assume_init() };
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///
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/// assert_eq!(*zero, 0)
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/// ```
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///
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/// [zeroed]: mem::MaybeUninit::zeroed
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#[cfg(not(no_global_oom_handling))]
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#[inline]
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#[unstable(feature = "new_zeroed_alloc", issue = "129396")]
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#[must_use]
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pub fn new_zeroed() -> Box<mem::MaybeUninit<T>> {
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Self::new_zeroed_in(Global)
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}
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/// Constructs a new `Pin<Box<T>>`. If `T` does not implement [`Unpin`], then
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/// `x` will be pinned in memory and unable to be moved.
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///
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/// Constructing and pinning of the `Box` can also be done in two steps: `Box::pin(x)`
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/// does the same as <code>[Box::into_pin]\([Box::new]\(x))</code>. Consider using
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/// [`into_pin`](Box::into_pin) if you already have a `Box<T>`, or if you want to
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/// construct a (pinned) `Box` in a different way than with [`Box::new`].
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#[cfg(not(no_global_oom_handling))]
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#[stable(feature = "pin", since = "1.33.0")]
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#[must_use]
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#[inline(always)]
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pub fn pin(x: T) -> Pin<Box<T>> {
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Box::new(x).into()
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}
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/// Allocates memory on the heap then places `x` into it,
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/// returning an error if the allocation fails
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///
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/// This doesn't actually allocate if `T` is zero-sized.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(allocator_api)]
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///
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/// let five = Box::try_new(5)?;
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/// # Ok::<(), std::alloc::AllocError>(())
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/// ```
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#[unstable(feature = "allocator_api", issue = "32838")]
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#[inline]
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pub fn try_new(x: T) -> Result<Self, AllocError> {
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Self::try_new_in(x, Global)
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}
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/// Constructs a new box with uninitialized contents on the heap,
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/// returning an error if the allocation fails
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///
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/// # Examples
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///
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/// ```
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/// #![feature(allocator_api)]
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///
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/// let mut five = Box::<u32>::try_new_uninit()?;
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/// // Deferred initialization:
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/// five.write(5);
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/// let five = unsafe { five.assume_init() };
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///
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/// assert_eq!(*five, 5);
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/// # Ok::<(), std::alloc::AllocError>(())
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/// ```
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#[unstable(feature = "allocator_api", issue = "32838")]
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// #[unstable(feature = "new_uninit", issue = "63291")]
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#[inline]
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pub fn try_new_uninit() -> Result<Box<mem::MaybeUninit<T>>, AllocError> {
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Box::try_new_uninit_in(Global)
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}
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/// Constructs a new `Box` with uninitialized contents, with the memory
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/// being filled with `0` bytes on the heap
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///
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/// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage
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/// of this method.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(allocator_api)]
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///
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/// let zero = Box::<u32>::try_new_zeroed()?;
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/// let zero = unsafe { zero.assume_init() };
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///
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/// assert_eq!(*zero, 0);
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/// # Ok::<(), std::alloc::AllocError>(())
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/// ```
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///
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/// [zeroed]: mem::MaybeUninit::zeroed
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#[unstable(feature = "allocator_api", issue = "32838")]
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// #[unstable(feature = "new_uninit", issue = "63291")]
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#[inline]
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pub fn try_new_zeroed() -> Result<Box<mem::MaybeUninit<T>>, AllocError> {
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Box::try_new_zeroed_in(Global)
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}
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}
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impl<T, A: Allocator> Box<T, A> {
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/// Allocates memory in the given allocator then places `x` into it.
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///
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/// This doesn't actually allocate if `T` is zero-sized.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(allocator_api)]
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///
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/// use std::alloc::System;
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///
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/// let five = Box::new_in(5, System);
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/// ```
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#[cfg(not(no_global_oom_handling))]
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#[unstable(feature = "allocator_api", issue = "32838")]
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#[must_use]
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#[inline]
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pub fn new_in(x: T, alloc: A) -> Self
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where
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A: Allocator,
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{
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let mut boxed = Self::new_uninit_in(alloc);
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boxed.write(x);
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unsafe { boxed.assume_init() }
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}
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/// Allocates memory in the given allocator then places `x` into it,
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/// returning an error if the allocation fails
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///
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/// This doesn't actually allocate if `T` is zero-sized.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(allocator_api)]
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///
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/// use std::alloc::System;
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///
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/// let five = Box::try_new_in(5, System)?;
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/// # Ok::<(), std::alloc::AllocError>(())
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/// ```
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#[unstable(feature = "allocator_api", issue = "32838")]
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#[inline]
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pub fn try_new_in(x: T, alloc: A) -> Result<Self, AllocError>
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where
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A: Allocator,
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{
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let mut boxed = Self::try_new_uninit_in(alloc)?;
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boxed.write(x);
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unsafe { Ok(boxed.assume_init()) }
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}
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|
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/// Constructs a new box with uninitialized contents in the provided allocator.
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///
|
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/// # Examples
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///
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/// ```
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/// #![feature(allocator_api)]
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///
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/// use std::alloc::System;
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///
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/// let mut five = Box::<u32, _>::new_uninit_in(System);
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/// // Deferred initialization:
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/// five.write(5);
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/// let five = unsafe { five.assume_init() };
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///
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/// 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)]
|
|
///
|
|
/// use std::alloc::System;
|
|
///
|
|
/// let mut five = Box::<u32, _>::try_new_uninit_in(System)?;
|
|
/// // Deferred initialization:
|
|
/// five.write(5);
|
|
/// let five = unsafe { 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 ptr = if T::IS_ZST {
|
|
NonNull::dangling()
|
|
} else {
|
|
let layout = Layout::new::<mem::MaybeUninit<T>>();
|
|
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)]
|
|
///
|
|
/// 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)]
|
|
///
|
|
/// 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 ptr = if T::IS_ZST {
|
|
NonNull::dangling()
|
|
} else {
|
|
let layout = Layout::new::<mem::MaybeUninit<T>>();
|
|
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
|
|
///
|
|
/// ```
|
|
/// let mut values = Box::<[u32]>::new_uninit_slice(3);
|
|
/// // Deferred initialization:
|
|
/// values[0].write(1);
|
|
/// values[1].write(2);
|
|
/// values[2].write(3);
|
|
/// let values = unsafe {values.assume_init() };
|
|
///
|
|
/// assert_eq!(*values, [1, 2, 3])
|
|
/// ```
|
|
#[cfg(not(no_global_oom_handling))]
|
|
#[stable(feature = "new_uninit", since = "1.82.0")]
|
|
#[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_zeroed_alloc)]
|
|
///
|
|
/// 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_zeroed_alloc", issue = "129396")]
|
|
#[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)]
|
|
///
|
|
/// let mut values = Box::<[u32]>::try_new_uninit_slice(3)?;
|
|
/// // Deferred initialization:
|
|
/// values[0].write(1);
|
|
/// values[1].write(2);
|
|
/// values[2].write(3);
|
|
/// let values = unsafe { 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> {
|
|
let ptr = if T::IS_ZST || len == 0 {
|
|
NonNull::dangling()
|
|
} else {
|
|
let layout = match Layout::array::<mem::MaybeUninit<T>>(len) {
|
|
Ok(l) => l,
|
|
Err(_) => return Err(AllocError),
|
|
};
|
|
Global.allocate(layout)?.cast()
|
|
};
|
|
unsafe { Ok(RawVec::from_raw_parts_in(ptr.as_ptr(), 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)]
|
|
///
|
|
/// 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> {
|
|
let ptr = if T::IS_ZST || len == 0 {
|
|
NonNull::dangling()
|
|
} else {
|
|
let layout = match Layout::array::<mem::MaybeUninit<T>>(len) {
|
|
Ok(l) => l,
|
|
Err(_) => return Err(AllocError),
|
|
};
|
|
Global.allocate_zeroed(layout)?.cast()
|
|
};
|
|
unsafe { Ok(RawVec::from_raw_parts_in(ptr.as_ptr(), len, Global).into_box(len)) }
|
|
}
|
|
|
|
/// Converts the boxed slice into a boxed array.
|
|
///
|
|
/// This operation does not reallocate; the underlying array of the slice is simply reinterpreted as an array type.
|
|
///
|
|
/// If `N` is not exactly equal to the length of `self`, then this method returns `None`.
|
|
#[unstable(feature = "slice_as_array", issue = "133508")]
|
|
#[inline]
|
|
#[must_use]
|
|
pub fn into_array<const N: usize>(self) -> Option<Box<[T; N]>> {
|
|
if self.len() == N {
|
|
let ptr = Self::into_raw(self) as *mut [T; N];
|
|
|
|
// SAFETY: The underlying array of a slice has the exact same layout as an actual array `[T; N]` if `N` is equal to the slice's length.
|
|
let me = unsafe { Box::from_raw(ptr) };
|
|
Some(me)
|
|
} else {
|
|
None
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T, A: Allocator> Box<[T], A> {
|
|
/// Constructs a new boxed slice with uninitialized contents in the provided allocator.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(allocator_api)]
|
|
///
|
|
/// use std::alloc::System;
|
|
///
|
|
/// let mut values = Box::<[u32], _>::new_uninit_slice_in(3, System);
|
|
/// // Deferred initialization:
|
|
/// values[0].write(1);
|
|
/// values[1].write(2);
|
|
/// values[2].write(3);
|
|
/// let values = unsafe { 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)]
|
|
///
|
|
/// 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) }
|
|
}
|
|
|
|
/// Constructs a new boxed slice with uninitialized contents in the provided allocator. Returns an error if
|
|
/// the allocation fails.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(allocator_api)]
|
|
///
|
|
/// use std::alloc::System;
|
|
///
|
|
/// let mut values = Box::<[u32], _>::try_new_uninit_slice_in(3, System)?;
|
|
/// // Deferred initialization:
|
|
/// values[0].write(1);
|
|
/// values[1].write(2);
|
|
/// values[2].write(3);
|
|
/// let values = unsafe { 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_in(
|
|
len: usize,
|
|
alloc: A,
|
|
) -> Result<Box<[mem::MaybeUninit<T>], A>, AllocError> {
|
|
let ptr = if T::IS_ZST || len == 0 {
|
|
NonNull::dangling()
|
|
} else {
|
|
let layout = match Layout::array::<mem::MaybeUninit<T>>(len) {
|
|
Ok(l) => l,
|
|
Err(_) => return Err(AllocError),
|
|
};
|
|
alloc.allocate(layout)?.cast()
|
|
};
|
|
unsafe { Ok(RawVec::from_raw_parts_in(ptr.as_ptr(), 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. 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)]
|
|
///
|
|
/// use std::alloc::System;
|
|
///
|
|
/// let values = Box::<[u32], _>::try_new_zeroed_slice_in(3, System)?;
|
|
/// 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_in(
|
|
len: usize,
|
|
alloc: A,
|
|
) -> Result<Box<[mem::MaybeUninit<T>], A>, AllocError> {
|
|
let ptr = if T::IS_ZST || len == 0 {
|
|
NonNull::dangling()
|
|
} else {
|
|
let layout = match Layout::array::<mem::MaybeUninit<T>>(len) {
|
|
Ok(l) => l,
|
|
Err(_) => return Err(AllocError),
|
|
};
|
|
alloc.allocate_zeroed(layout)?.cast()
|
|
};
|
|
unsafe { Ok(RawVec::from_raw_parts_in(ptr.as_ptr(), 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
|
|
///
|
|
/// ```
|
|
/// let mut five = Box::<u32>::new_uninit();
|
|
/// // Deferred initialization:
|
|
/// five.write(5);
|
|
/// let five: Box<u32> = unsafe { five.assume_init() };
|
|
///
|
|
/// assert_eq!(*five, 5)
|
|
/// ```
|
|
#[stable(feature = "new_uninit", since = "1.82.0")]
|
|
#[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
|
|
///
|
|
/// ```
|
|
/// 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);
|
|
/// }
|
|
/// ```
|
|
#[stable(feature = "box_uninit_write", since = "CURRENT_RUSTC_VERSION")]
|
|
#[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
|
|
///
|
|
/// ```
|
|
/// let mut values = Box::<[u32]>::new_uninit_slice(3);
|
|
/// // Deferred initialization:
|
|
/// values[0].write(1);
|
|
/// values[1].write(2);
|
|
/// values[2].write(3);
|
|
/// let values = unsafe { values.assume_init() };
|
|
///
|
|
/// assert_eq!(*values, [1, 2, 3])
|
|
/// ```
|
|
#[stable(feature = "new_uninit", since = "1.82.0")]
|
|
#[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 raw pointer must point to a block of memory allocated by the global allocator.
|
|
///
|
|
/// 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
|
|
#[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) }
|
|
}
|
|
|
|
/// Constructs a box from a `NonNull` pointer.
|
|
///
|
|
/// After calling this function, the `NonNull` 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 `NonNull` pointer.
|
|
///
|
|
/// The non-null pointer must point to a block of memory allocated by the global allocator.
|
|
///
|
|
/// The safety conditions are described in the [memory layout] section.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Recreate a `Box` which was previously converted to a `NonNull`
|
|
/// pointer using [`Box::into_non_null`]:
|
|
/// ```
|
|
/// #![feature(box_vec_non_null)]
|
|
///
|
|
/// let x = Box::new(5);
|
|
/// let non_null = Box::into_non_null(x);
|
|
/// let x = unsafe { Box::from_non_null(non_null) };
|
|
/// ```
|
|
/// Manually create a `Box` from scratch by using the global allocator:
|
|
/// ```
|
|
/// #![feature(box_vec_non_null)]
|
|
///
|
|
/// use std::alloc::{alloc, Layout};
|
|
/// use std::ptr::NonNull;
|
|
///
|
|
/// unsafe {
|
|
/// let non_null = NonNull::new(alloc(Layout::new::<i32>()).cast::<i32>())
|
|
/// .expect("allocation failed");
|
|
/// // In general .write is required to avoid attempting to destruct
|
|
/// // the (uninitialized) previous contents of `non_null`.
|
|
/// non_null.write(5);
|
|
/// let x = Box::from_non_null(non_null);
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// [memory layout]: self#memory-layout
|
|
#[unstable(feature = "box_vec_non_null", reason = "new API", issue = "130364")]
|
|
#[inline]
|
|
#[must_use = "call `drop(Box::from_non_null(ptr))` if you intend to drop the `Box`"]
|
|
pub unsafe fn from_non_null(ptr: NonNull<T>) -> Self {
|
|
unsafe { Self::from_raw(ptr.as_ptr()) }
|
|
}
|
|
}
|
|
|
|
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.
|
|
///
|
|
/// The raw pointer must point to a block of memory allocated by `alloc`.
|
|
///
|
|
/// # 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
|
|
#[unstable(feature = "allocator_api", issue = "32838")]
|
|
#[inline]
|
|
pub unsafe fn from_raw_in(raw: *mut T, alloc: A) -> Self {
|
|
Box(unsafe { Unique::new_unchecked(raw) }, alloc)
|
|
}
|
|
|
|
/// Constructs a box from a `NonNull` pointer in the given allocator.
|
|
///
|
|
/// After calling this function, the `NonNull` 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 non-null pointer must point to a block of memory allocated by `alloc`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Recreate a `Box` which was previously converted to a `NonNull` pointer
|
|
/// using [`Box::into_non_null_with_allocator`]:
|
|
/// ```
|
|
/// #![feature(allocator_api, box_vec_non_null)]
|
|
///
|
|
/// use std::alloc::System;
|
|
///
|
|
/// let x = Box::new_in(5, System);
|
|
/// let (non_null, alloc) = Box::into_non_null_with_allocator(x);
|
|
/// let x = unsafe { Box::from_non_null_in(non_null, alloc) };
|
|
/// ```
|
|
/// Manually create a `Box` from scratch by using the system allocator:
|
|
/// ```
|
|
/// #![feature(allocator_api, box_vec_non_null, slice_ptr_get)]
|
|
///
|
|
/// use std::alloc::{Allocator, Layout, System};
|
|
///
|
|
/// unsafe {
|
|
/// let non_null = System.allocate(Layout::new::<i32>())?.cast::<i32>();
|
|
/// // In general .write is required to avoid attempting to destruct
|
|
/// // the (uninitialized) previous contents of `non_null`.
|
|
/// non_null.write(5);
|
|
/// let x = Box::from_non_null_in(non_null, System);
|
|
/// }
|
|
/// # Ok::<(), std::alloc::AllocError>(())
|
|
/// ```
|
|
///
|
|
/// [memory layout]: self#memory-layout
|
|
#[unstable(feature = "allocator_api", issue = "32838")]
|
|
// #[unstable(feature = "box_vec_non_null", reason = "new API", issue = "130364")]
|
|
#[inline]
|
|
pub unsafe fn from_non_null_in(raw: NonNull<T>, alloc: A) -> Self {
|
|
// SAFETY: guaranteed by the caller.
|
|
unsafe { Box::from_raw_in(raw.as_ptr(), 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 ptr = Box::into_raw(x);
|
|
/// unsafe {
|
|
/// ptr::drop_in_place(ptr);
|
|
/// dealloc(ptr as *mut u8, Layout::new::<String>());
|
|
/// }
|
|
/// ```
|
|
/// Note: This is equivalent to the following:
|
|
/// ```
|
|
/// let x = Box::new(String::from("Hello"));
|
|
/// let ptr = Box::into_raw(x);
|
|
/// unsafe {
|
|
/// drop(Box::from_raw(ptr));
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// [memory layout]: self#memory-layout
|
|
#[must_use = "losing the pointer will leak memory"]
|
|
#[stable(feature = "box_raw", since = "1.4.0")]
|
|
#[inline]
|
|
pub fn into_raw(b: Self) -> *mut T {
|
|
// Make sure Miri realizes that we transition from a noalias pointer to a raw pointer here.
|
|
unsafe { &raw mut *&mut *Self::into_raw_with_allocator(b).0 }
|
|
}
|
|
|
|
/// Consumes the `Box`, returning a wrapped `NonNull` pointer.
|
|
///
|
|
/// The pointer will be properly aligned.
|
|
///
|
|
/// 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 `NonNull` pointer back into a `Box` with the
|
|
/// [`Box::from_non_null`] 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_non_null(b)` instead of `b.into_non_null()`.
|
|
/// This is so that there is no conflict with a method on the inner type.
|
|
///
|
|
/// # Examples
|
|
/// Converting the `NonNull` pointer back into a `Box` with [`Box::from_non_null`]
|
|
/// for automatic cleanup:
|
|
/// ```
|
|
/// #![feature(box_vec_non_null)]
|
|
///
|
|
/// let x = Box::new(String::from("Hello"));
|
|
/// let non_null = Box::into_non_null(x);
|
|
/// let x = unsafe { Box::from_non_null(non_null) };
|
|
/// ```
|
|
/// Manual cleanup by explicitly running the destructor and deallocating
|
|
/// the memory:
|
|
/// ```
|
|
/// #![feature(box_vec_non_null)]
|
|
///
|
|
/// use std::alloc::{dealloc, Layout};
|
|
///
|
|
/// let x = Box::new(String::from("Hello"));
|
|
/// let non_null = Box::into_non_null(x);
|
|
/// unsafe {
|
|
/// non_null.drop_in_place();
|
|
/// dealloc(non_null.as_ptr().cast::<u8>(), Layout::new::<String>());
|
|
/// }
|
|
/// ```
|
|
/// Note: This is equivalent to the following:
|
|
/// ```
|
|
/// #![feature(box_vec_non_null)]
|
|
///
|
|
/// let x = Box::new(String::from("Hello"));
|
|
/// let non_null = Box::into_non_null(x);
|
|
/// unsafe {
|
|
/// drop(Box::from_non_null(non_null));
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// [memory layout]: self#memory-layout
|
|
#[must_use = "losing the pointer will leak memory"]
|
|
#[unstable(feature = "box_vec_non_null", reason = "new API", issue = "130364")]
|
|
#[inline]
|
|
pub fn into_non_null(b: Self) -> NonNull<T> {
|
|
// SAFETY: `Box` is guaranteed to be non-null.
|
|
unsafe { NonNull::new_unchecked(Self::into_raw(b)) }
|
|
}
|
|
|
|
/// 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
|
|
#[must_use = "losing the pointer will leak memory"]
|
|
#[unstable(feature = "allocator_api", issue = "32838")]
|
|
#[inline]
|
|
pub fn into_raw_with_allocator(b: Self) -> (*mut T, A) {
|
|
let mut b = mem::ManuallyDrop::new(b);
|
|
// We carefully get the raw pointer out in a way that Miri's aliasing model understands what
|
|
// is happening: using the primitive "deref" of `Box`. In case `A` is *not* `Global`, we
|
|
// want *no* aliasing requirements here!
|
|
// In case `A` *is* `Global`, this does not quite have the right behavior; `into_raw`
|
|
// works around that.
|
|
let ptr = &raw mut **b;
|
|
let alloc = unsafe { ptr::read(&b.1) };
|
|
(ptr, alloc)
|
|
}
|
|
|
|
/// Consumes the `Box`, returning a wrapped `NonNull` pointer and the allocator.
|
|
///
|
|
/// The pointer will be properly aligned.
|
|
///
|
|
/// 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 `NonNull` pointer back into a `Box` with the
|
|
/// [`Box::from_non_null_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_non_null_with_allocator(b)` instead of
|
|
/// `b.into_non_null_with_allocator()`. This is so that there is no
|
|
/// conflict with a method on the inner type.
|
|
///
|
|
/// # Examples
|
|
/// Converting the `NonNull` pointer back into a `Box` with
|
|
/// [`Box::from_non_null_in`] for automatic cleanup:
|
|
/// ```
|
|
/// #![feature(allocator_api, box_vec_non_null)]
|
|
///
|
|
/// use std::alloc::System;
|
|
///
|
|
/// let x = Box::new_in(String::from("Hello"), System);
|
|
/// let (non_null, alloc) = Box::into_non_null_with_allocator(x);
|
|
/// let x = unsafe { Box::from_non_null_in(non_null, alloc) };
|
|
/// ```
|
|
/// Manual cleanup by explicitly running the destructor and deallocating
|
|
/// the memory:
|
|
/// ```
|
|
/// #![feature(allocator_api, box_vec_non_null)]
|
|
///
|
|
/// use std::alloc::{Allocator, Layout, System};
|
|
///
|
|
/// let x = Box::new_in(String::from("Hello"), System);
|
|
/// let (non_null, alloc) = Box::into_non_null_with_allocator(x);
|
|
/// unsafe {
|
|
/// non_null.drop_in_place();
|
|
/// alloc.deallocate(non_null.cast::<u8>(), Layout::new::<String>());
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// [memory layout]: self#memory-layout
|
|
#[must_use = "losing the pointer will leak memory"]
|
|
#[unstable(feature = "allocator_api", issue = "32838")]
|
|
// #[unstable(feature = "box_vec_non_null", reason = "new API", issue = "130364")]
|
|
#[inline]
|
|
pub fn into_non_null_with_allocator(b: Self) -> (NonNull<T>, A) {
|
|
let (ptr, alloc) = Box::into_raw_with_allocator(b);
|
|
// SAFETY: `Box` is guaranteed to be non-null.
|
|
unsafe { (NonNull::new_unchecked(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) {
|
|
let (ptr, alloc) = Box::into_raw_with_allocator(b);
|
|
unsafe { (Unique::from(&mut *ptr), alloc) }
|
|
}
|
|
|
|
/// Returns a raw mutable pointer to the `Box`'s contents.
|
|
///
|
|
/// The caller must ensure that the `Box` outlives the pointer this
|
|
/// function returns, or else it will end up dangling.
|
|
///
|
|
/// This method guarantees that for the purpose of the aliasing model, this method
|
|
/// does not materialize a reference to the underlying memory, and thus the returned pointer
|
|
/// will remain valid when mixed with other calls to [`as_ptr`] and [`as_mut_ptr`].
|
|
/// Note that calling other methods that materialize references to the memory
|
|
/// may still invalidate this pointer.
|
|
/// See the example below for how this guarantee can be used.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Due to the aliasing guarantee, the following code is legal:
|
|
///
|
|
/// ```rust
|
|
/// #![feature(box_as_ptr)]
|
|
///
|
|
/// unsafe {
|
|
/// let mut b = Box::new(0);
|
|
/// let ptr1 = Box::as_mut_ptr(&mut b);
|
|
/// ptr1.write(1);
|
|
/// let ptr2 = Box::as_mut_ptr(&mut b);
|
|
/// ptr2.write(2);
|
|
/// // Notably, the write to `ptr2` did *not* invalidate `ptr1`:
|
|
/// ptr1.write(3);
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// [`as_mut_ptr`]: Self::as_mut_ptr
|
|
/// [`as_ptr`]: Self::as_ptr
|
|
#[unstable(feature = "box_as_ptr", issue = "129090")]
|
|
#[rustc_never_returns_null_ptr]
|
|
#[rustc_as_ptr]
|
|
#[inline]
|
|
pub fn as_mut_ptr(b: &mut Self) -> *mut T {
|
|
// This is a primitive deref, not going through `DerefMut`, and therefore not materializing
|
|
// any references.
|
|
&raw mut **b
|
|
}
|
|
|
|
/// Returns a raw pointer to the `Box`'s contents.
|
|
///
|
|
/// The caller must ensure that the `Box` outlives the pointer this
|
|
/// function returns, or else it will end up dangling.
|
|
///
|
|
/// 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 `Box`, use [`as_mut_ptr`].
|
|
///
|
|
/// This method guarantees that for the purpose of the aliasing model, this method
|
|
/// does not materialize a reference to the underlying memory, and thus the returned pointer
|
|
/// will remain valid when mixed with other calls to [`as_ptr`] and [`as_mut_ptr`].
|
|
/// Note that calling other methods that materialize mutable references to the memory,
|
|
/// as well as writing to this memory, may still invalidate this pointer.
|
|
/// See the example below for how this guarantee can be used.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Due to the aliasing guarantee, the following code is legal:
|
|
///
|
|
/// ```rust
|
|
/// #![feature(box_as_ptr)]
|
|
///
|
|
/// unsafe {
|
|
/// let mut v = Box::new(0);
|
|
/// let ptr1 = Box::as_ptr(&v);
|
|
/// let ptr2 = Box::as_mut_ptr(&mut v);
|
|
/// let _val = ptr2.read();
|
|
/// // No write to this memory has happened yet, so `ptr1` is still valid.
|
|
/// let _val = ptr1.read();
|
|
/// // However, once we do a write...
|
|
/// ptr2.write(1);
|
|
/// // ... `ptr1` is no longer valid.
|
|
/// // This would be UB: let _val = ptr1.read();
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// [`as_mut_ptr`]: Self::as_mut_ptr
|
|
/// [`as_ptr`]: Self::as_ptr
|
|
#[unstable(feature = "box_as_ptr", issue = "129090")]
|
|
#[rustc_never_returns_null_ptr]
|
|
#[rustc_as_ptr]
|
|
#[inline]
|
|
pub fn as_ptr(b: &Self) -> *const T {
|
|
// This is a primitive deref, not going through `DerefMut`, and therefore not materializing
|
|
// any references.
|
|
&raw const **b
|
|
}
|
|
|
|
/// 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")]
|
|
#[inline]
|
|
pub 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);
|
|
/// # // FIXME(https://github.com/rust-lang/miri/issues/3670):
|
|
/// # // use -Zmiri-disable-leak-check instead of unleaking in tests meant to leak.
|
|
/// # drop(unsafe { Box::from_raw(static_ref) });
|
|
/// ```
|
|
///
|
|
/// 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]);
|
|
/// # // FIXME(https://github.com/rust-lang/miri/issues/3670):
|
|
/// # // use -Zmiri-disable-leak-check instead of unleaking in tests meant to leak.
|
|
/// # drop(unsafe { Box::from_raw(static_ref) });
|
|
/// ```
|
|
#[stable(feature = "box_leak", since = "1.26.0")]
|
|
#[inline]
|
|
pub fn leak<'a>(b: Self) -> &'a mut T
|
|
where
|
|
A: 'a,
|
|
{
|
|
unsafe { &mut *Box::into_raw(b) }
|
|
}
|
|
|
|
/// 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")]
|
|
pub 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> {
|
|
#[inline]
|
|
fn drop(&mut self) {
|
|
// the T in the Box is dropped by the compiler before the destructor is run
|
|
|
|
let ptr = self.0;
|
|
|
|
unsafe {
|
|
let layout = Layout::for_value_raw(ptr.as_ptr());
|
|
if layout.size() != 0 {
|
|
self.1.deallocate(From::from(ptr.cast()), layout);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
#[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 {
|
|
let mut x: Box<mem::MaybeUninit<T>> = Box::new_uninit();
|
|
unsafe {
|
|
// SAFETY: `x` is valid for writing and has the same layout as `T`.
|
|
// If `T::default()` panics, dropping `x` will just deallocate the Box as `MaybeUninit<T>`
|
|
// does not have a destructor.
|
|
//
|
|
// We use `ptr::write` as `MaybeUninit::write` creates
|
|
// extra stack copies of `T` in debug mode.
|
|
//
|
|
// See https://github.com/rust-lang/rust/issues/136043 for more context.
|
|
ptr::write(&raw mut *x as *mut T, T::default());
|
|
// SAFETY: `x` was just initialized above.
|
|
x.assume_init()
|
|
}
|
|
}
|
|
}
|
|
|
|
#[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).clone_to_uninit(boxed.as_mut_ptr().cast());
|
|
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<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()
|
|
}
|
|
|
|
/// Copies `source`'s contents into `self` without creating a new allocation,
|
|
/// so long as the two are of the same length.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x = Box::new([5, 6, 7]);
|
|
/// let mut y = Box::new([8, 9, 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);
|
|
/// ```
|
|
fn clone_from(&mut self, source: &Self) {
|
|
if self.len() == source.len() {
|
|
self.clone_from_slice(&source);
|
|
} else {
|
|
*self = source.clone();
|
|
}
|
|
}
|
|
}
|
|
|
|
#[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)
|
|
}
|
|
}
|
|
|
|
#[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 = "deref_pure_trait", issue = "87121")]
|
|
unsafe impl<T: ?Sized, A: Allocator> DerefPure for Box<T, A> {}
|
|
|
|
#[unstable(feature = "legacy_receiver_trait", issue = "none")]
|
|
impl<T: ?Sized, A: Allocator> LegacyReceiver for Box<T, 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)
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "async_closure", since = "1.85.0")]
|
|
impl<Args: Tuple, F: AsyncFnOnce<Args> + ?Sized, A: Allocator> AsyncFnOnce<Args> for Box<F, A> {
|
|
type Output = F::Output;
|
|
type CallOnceFuture = F::CallOnceFuture;
|
|
|
|
extern "rust-call" fn async_call_once(self, args: Args) -> Self::CallOnceFuture {
|
|
F::async_call_once(*self, args)
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "async_closure", since = "1.85.0")]
|
|
impl<Args: Tuple, F: AsyncFnMut<Args> + ?Sized, A: Allocator> AsyncFnMut<Args> for Box<F, A> {
|
|
type CallRefFuture<'a>
|
|
= F::CallRefFuture<'a>
|
|
where
|
|
Self: 'a;
|
|
|
|
extern "rust-call" fn async_call_mut(&mut self, args: Args) -> Self::CallRefFuture<'_> {
|
|
F::async_call_mut(self, args)
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "async_closure", since = "1.85.0")]
|
|
impl<Args: Tuple, F: AsyncFn<Args> + ?Sized, A: Allocator> AsyncFn<Args> for Box<F, A> {
|
|
extern "rust-call" fn async_call(&self, args: Args) -> Self::CallRefFuture<'_> {
|
|
F::async_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 = "pin_coerce_unsized_trait", issue = "123430")]
|
|
unsafe impl<T: ?Sized, A: Allocator> PinCoerceUnsized for Box<T, A> {}
|
|
|
|
// It is quite crucial that we only allow the `Global` allocator here.
|
|
// Handling arbitrary custom allocators (which can affect the `Box` layout heavily!)
|
|
// would need a lot of codegen and interpreter adjustments.
|
|
#[unstable(feature = "dispatch_from_dyn", issue = "none")]
|
|
impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Box<U>> for Box<T, Global> {}
|
|
|
|
#[stable(feature = "box_borrow", since = "1.1.0")]
|
|
impl<T: ?Sized, A: Allocator> Borrow<T> for Box<T, A> {
|
|
fn borrow(&self) -> &T {
|
|
&**self
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "box_borrow", since = "1.1.0")]
|
|
impl<T: ?Sized, A: Allocator> 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> {}
|
|
|
|
#[unstable(feature = "coroutine_trait", issue = "43122")]
|
|
impl<G: ?Sized + Coroutine<R> + Unpin, R, A: Allocator> Coroutine<R> for Box<G, A> {
|
|
type Yield = G::Yield;
|
|
type Return = G::Return;
|
|
|
|
fn resume(mut self: Pin<&mut Self>, arg: R) -> CoroutineState<Self::Yield, Self::Return> {
|
|
G::resume(Pin::new(&mut *self), arg)
|
|
}
|
|
}
|
|
|
|
#[unstable(feature = "coroutine_trait", issue = "43122")]
|
|
impl<G: ?Sized + Coroutine<R>, R, A: Allocator> Coroutine<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) -> CoroutineState<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> {
|
|
type Output = F::Output;
|
|
|
|
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
|
|
F::poll(Pin::new(&mut *self), cx)
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "box_error", since = "1.8.0")]
|
|
impl<E: Error> Error for Box<E> {
|
|
#[allow(deprecated, deprecated_in_future)]
|
|
fn description(&self) -> &str {
|
|
Error::description(&**self)
|
|
}
|
|
|
|
#[allow(deprecated)]
|
|
fn cause(&self) -> Option<&dyn Error> {
|
|
Error::cause(&**self)
|
|
}
|
|
|
|
fn source(&self) -> Option<&(dyn Error + 'static)> {
|
|
Error::source(&**self)
|
|
}
|
|
|
|
fn provide<'b>(&'b self, request: &mut error::Request<'b>) {
|
|
Error::provide(&**self, request);
|
|
}
|
|
}
|
|
|
|
#[unstable(feature = "pointer_like_trait", issue = "none")]
|
|
impl<T> PointerLike for Box<T> {}
|