685 lines
20 KiB
Rust
685 lines
20 KiB
Rust
//! A pointer type for bump allocation.
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//!
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//! [`Box<'a, T>`] provides the simplest form of
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//! bump allocation in `bumpalo`. Boxes provide ownership for this allocation, and
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//! drop their contents when they go out of scope.
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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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//! use bumpalo::{Bump, boxed::Box};
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//!
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//! let b = Bump::new();
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//!
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//! let val: u8 = 5;
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//! let boxed: Box<u8> = Box::new_in(val, &b);
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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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//! use bumpalo::{Bump, boxed::Box};
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//!
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//! let b = Bump::new();
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//!
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//! let boxed: Box<u8> = Box::new_in(5, &b);
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//! let val: u8 = *boxed;
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//! ```
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//!
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//! Running [`Drop`] implementations on bump-allocated values:
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//!
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//! ```
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//! use bumpalo::{Bump, boxed::Box};
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//! use std::sync::atomic::{AtomicUsize, Ordering};
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//!
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//! static NUM_DROPPED: AtomicUsize = AtomicUsize::new(0);
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//!
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//! struct CountDrops;
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//!
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//! impl Drop for CountDrops {
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//! fn drop(&mut self) {
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//! NUM_DROPPED.fetch_add(1, Ordering::SeqCst);
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//! }
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//! }
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//!
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//! // Create a new bump arena.
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//! let bump = Bump::new();
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//!
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//! // Create a `CountDrops` inside the bump arena.
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//! let mut c = Box::new_in(CountDrops, &bump);
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//!
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//! // No `CountDrops` have been dropped yet.
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//! assert_eq!(NUM_DROPPED.load(Ordering::SeqCst), 0);
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//!
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//! // Drop our `Box<CountDrops>`.
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//! drop(c);
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//!
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//! // Its `Drop` implementation was run, and so `NUM_DROPS` has been incremented.
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//! assert_eq!(NUM_DROPPED.load(Ordering::SeqCst), 1);
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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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//! use bumpalo::{Bump, boxed::Box};
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//!
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//! let b = Bump::new();
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//!
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//! #[derive(Debug)]
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//! enum List<'a, T> {
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//! Cons(T, Box<'a, List<'a, 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_in(List::Cons(2, Box::new_in(List::Nil, &b)), &b));
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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<'a, 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 provided [`Bump`] allocator for
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//! its allocation. It is valid to convert both ways between a [`Box`] and a
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//! pointer allocated with the [`Bump`] allocator, given that the
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//! [`Layout`] used with the allocator is correct for the type. More precisely,
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//! a `value: *mut T` that has been allocated with the [`Bump`] allocator
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//! with `Layout::for_value(&*value)` may be converted into a box using
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//! [`Box::<T>::from_raw(value)`]. Conversely, the memory backing a `value: *mut
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//! T` obtained from [`Box::<T>::into_raw`] will be deallocated by the
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//! [`Bump`] allocator with [`Layout::for_value(&*value)`].
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//!
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//! Note that roundtrip `Box::from_raw(Box::into_raw(b))` looses the lifetime bound to the
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//! [`Bump`] immutable borrow which guarantees that the allocator will not be reset
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//! and memory will not be freed.
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//!
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//! [dereferencing]: https://doc.rust-lang.org/std/ops/trait.Deref.html
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//! [`Box`]: struct.Box.html
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//! [`Box<'a, T>`]: struct.Box.html
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//! [`Box::<T>::from_raw(value)`]: struct.Box.html#method.from_raw
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//! [`Box::<T>::into_raw`]: struct.Box.html#method.into_raw
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//! [`Bump`]: ../struct.Bump.html
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//! [`Drop`]: https://doc.rust-lang.org/std/ops/trait.Drop.html
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//! [`Layout`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html
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//! [`Layout::for_value(&*value)`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.for_value
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use {
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crate::Bump,
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{
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core::{
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any::Any,
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borrow,
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cmp::Ordering,
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convert::TryFrom,
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future::Future,
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hash::{Hash, Hasher},
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iter::FusedIterator,
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mem,
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ops::{Deref, DerefMut},
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pin::Pin,
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task::{Context, Poll},
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},
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core_alloc::fmt,
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},
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};
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/// An owned pointer to a bump-allocated `T` value, that runs `Drop`
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/// implementations.
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///
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/// See the [module-level documentation][crate::boxed] for more details.
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#[repr(transparent)]
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pub struct Box<'a, T: ?Sized>(&'a mut T);
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impl<'a, T> Box<'a, 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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/// use bumpalo::{Bump, boxed::Box};
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///
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/// let b = Bump::new();
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///
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/// let five = Box::new_in(5, &b);
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/// ```
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#[inline(always)]
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pub fn new_in(x: T, a: &'a Bump) -> Box<'a, T> {
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Box(a.alloc(x))
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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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#[inline(always)]
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pub fn pin_in(x: T, a: &'a Bump) -> Pin<Box<'a, T>> {
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Box(a.alloc(x)).into()
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}
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/// Consumes the `Box`, returning the wrapped value.
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///
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/// # Examples
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///
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/// ```
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/// use bumpalo::{Bump, boxed::Box};
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///
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/// let b = Bump::new();
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///
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/// let hello = Box::new_in("hello".to_owned(), &b);
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/// assert_eq!(Box::into_inner(hello), "hello");
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/// ```
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pub fn into_inner(b: Box<'a, T>) -> T {
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// `Box::into_raw` returns a pointer that is properly aligned and non-null.
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// The underlying `Bump` only frees the memory, but won't call the destructor.
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unsafe { core::ptr::read(Box::into_raw(b)) }
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}
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}
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impl<'a, T: ?Sized> Box<'a, T> {
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/// Constructs a box from a raw pointer.
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///
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/// After calling this function, the raw pointer is owned by the
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/// resulting `Box`. Specifically, the `Box` destructor will call
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/// the destructor of `T` and free the allocated memory. For this
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/// to be safe, the memory must have been allocated in accordance
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/// with the memory layout used by `Box` .
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///
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/// # Safety
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///
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/// This function is unsafe because improper use may lead to
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/// memory problems. For example, a double-free may occur if the
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/// function is called twice on the same raw pointer.
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///
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/// # Examples
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///
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/// Recreate a `Box` which was previously converted to a raw pointer
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/// using [`Box::into_raw`]:
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/// ```
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/// use bumpalo::{Bump, boxed::Box};
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///
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/// let b = Bump::new();
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///
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/// let x = Box::new_in(5, &b);
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/// let ptr = Box::into_raw(x);
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/// let x = unsafe { Box::from_raw(ptr) }; // Note that new `x`'s lifetime is unbound. It must be bound to the `b` immutable borrow before `b` is reset.
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/// ```
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/// Manually create a `Box` from scratch by using the bump allocator:
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/// ```
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/// use std::alloc::{alloc, Layout};
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/// use bumpalo::{Bump, boxed::Box};
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///
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/// let b = Bump::new();
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///
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/// unsafe {
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/// let ptr = b.alloc_layout(Layout::new::<i32>()).as_ptr() as *mut i32;
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/// *ptr = 5;
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/// let x = Box::from_raw(ptr); // Note that `x`'s lifetime is unbound. It must be bound to the `b` immutable borrow before `b` is reset.
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/// }
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/// ```
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#[inline]
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pub unsafe fn from_raw(raw: *mut T) -> Self {
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Box(&mut *raw)
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}
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/// Consumes the `Box`, returning a wrapped raw pointer.
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///
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/// The pointer will be properly aligned and non-null.
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///
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/// After calling this function, the caller is responsible for the
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/// value previously managed by the `Box`. In particular, the
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/// caller should properly destroy `T`. The easiest way to
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/// do this is to convert the raw pointer back into a `Box` with the
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/// [`Box::from_raw`] function, allowing the `Box` destructor to perform
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/// the cleanup.
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///
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/// Note: this is an associated function, which means that you have
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/// to call it as `Box::into_raw(b)` instead of `b.into_raw()`. This
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/// is so that there is no conflict with a method on the inner type.
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///
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/// # Examples
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///
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/// Converting the raw pointer back into a `Box` with [`Box::from_raw`]
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/// for automatic cleanup:
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/// ```
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/// use bumpalo::{Bump, boxed::Box};
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///
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/// let b = Bump::new();
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///
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/// let x = Box::new_in(String::from("Hello"), &b);
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/// let ptr = Box::into_raw(x);
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/// let x = unsafe { Box::from_raw(ptr) }; // Note that new `x`'s lifetime is unbound. It must be bound to the `b` immutable borrow before `b` is reset.
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/// ```
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/// Manual cleanup by explicitly running the destructor:
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/// ```
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/// use std::ptr;
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/// use bumpalo::{Bump, boxed::Box};
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///
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/// let b = Bump::new();
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///
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/// let mut x = Box::new_in(String::from("Hello"), &b);
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/// let p = Box::into_raw(x);
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/// unsafe {
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/// ptr::drop_in_place(p);
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/// }
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/// ```
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#[inline]
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pub fn into_raw(b: Box<'a, T>) -> *mut T {
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let ptr = b.0 as *mut T;
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mem::forget(b);
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ptr
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}
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/// Consumes and leaks the `Box`, returning a mutable reference,
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/// `&'a mut T`. Note that the type `T` must outlive the chosen lifetime
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/// `'a`. If the type has only static references, or none at all, then this
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/// may be chosen to be `'static`.
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///
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/// This function is mainly useful for data that lives for the remainder of
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/// the program's life. Dropping the returned reference will cause a memory
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/// leak. If this is not acceptable, the reference should first be wrapped
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/// with the [`Box::from_raw`] function producing a `Box`. This `Box` can
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/// then be dropped which will properly destroy `T` and release the
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/// allocated memory.
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///
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/// Note: this is an associated function, which means that you have
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/// to call it as `Box::leak(b)` instead of `b.leak()`. This
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/// is so that there is no conflict with a method on the inner type.
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///
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/// # Examples
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///
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/// Simple usage:
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///
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/// ```
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/// use bumpalo::{Bump, boxed::Box};
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///
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/// let b = Bump::new();
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///
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/// let x = Box::new_in(41, &b);
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/// let reference: &mut usize = Box::leak(x);
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/// *reference += 1;
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/// assert_eq!(*reference, 42);
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/// ```
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///
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///```
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/// # #[cfg(feature = "collections")]
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/// # {
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/// use bumpalo::{Bump, boxed::Box, vec};
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///
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/// let b = Bump::new();
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///
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/// let x = vec![in &b; 1, 2, 3].into_boxed_slice();
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/// let reference = Box::leak(x);
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/// reference[0] = 4;
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/// assert_eq!(*reference, [4, 2, 3]);
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/// # }
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///```
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#[inline]
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pub fn leak(b: Box<'a, T>) -> &'a mut T {
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unsafe { &mut *Box::into_raw(b) }
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}
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}
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impl<'a, T: ?Sized> Drop for Box<'a, T> {
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fn drop(&mut self) {
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unsafe {
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// `Box` owns value of `T`, but not memory behind it.
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core::ptr::drop_in_place(self.0);
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}
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}
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}
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impl<'a, T> Default for Box<'a, [T]> {
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fn default() -> Box<'a, [T]> {
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// It should be OK to `drop_in_place` empty slice of anything.
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Box(&mut [])
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}
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}
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impl<'a> Default for Box<'a, str> {
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fn default() -> Box<'a, str> {
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// Empty slice is valid string.
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// It should be OK to `drop_in_place` empty str.
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unsafe { Box::from_raw(Box::into_raw(Box::<[u8]>::default()) as *mut str) }
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}
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}
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impl<'a, 'b, T: ?Sized + PartialEq> PartialEq<Box<'b, T>> for Box<'a, T> {
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#[inline]
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fn eq(&self, other: &Box<'b, T>) -> bool {
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PartialEq::eq(&**self, &**other)
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}
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#[inline]
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fn ne(&self, other: &Box<'b, T>) -> bool {
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PartialEq::ne(&**self, &**other)
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}
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}
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impl<'a, 'b, T: ?Sized + PartialOrd> PartialOrd<Box<'b, T>> for Box<'a, T> {
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#[inline]
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fn partial_cmp(&self, other: &Box<'b, T>) -> Option<Ordering> {
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PartialOrd::partial_cmp(&**self, &**other)
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}
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#[inline]
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fn lt(&self, other: &Box<'b, T>) -> bool {
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PartialOrd::lt(&**self, &**other)
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}
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#[inline]
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fn le(&self, other: &Box<'b, T>) -> bool {
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PartialOrd::le(&**self, &**other)
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}
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#[inline]
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fn ge(&self, other: &Box<'b, T>) -> bool {
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PartialOrd::ge(&**self, &**other)
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}
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#[inline]
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fn gt(&self, other: &Box<'b, T>) -> bool {
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PartialOrd::gt(&**self, &**other)
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}
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}
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impl<'a, T: ?Sized + Ord> Ord for Box<'a, T> {
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#[inline]
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fn cmp(&self, other: &Box<'a, T>) -> Ordering {
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Ord::cmp(&**self, &**other)
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}
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}
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impl<'a, T: ?Sized + Eq> Eq for Box<'a, T> {}
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impl<'a, T: ?Sized + Hash> Hash for Box<'a, T> {
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fn hash<H: Hasher>(&self, state: &mut H) {
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(**self).hash(state);
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}
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}
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impl<'a, T: ?Sized + Hasher> Hasher for Box<'a, T> {
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fn finish(&self) -> u64 {
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(**self).finish()
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}
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fn write(&mut self, bytes: &[u8]) {
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(**self).write(bytes)
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}
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fn write_u8(&mut self, i: u8) {
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(**self).write_u8(i)
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}
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fn write_u16(&mut self, i: u16) {
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(**self).write_u16(i)
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}
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fn write_u32(&mut self, i: u32) {
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(**self).write_u32(i)
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}
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fn write_u64(&mut self, i: u64) {
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(**self).write_u64(i)
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}
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fn write_u128(&mut self, i: u128) {
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(**self).write_u128(i)
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}
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fn write_usize(&mut self, i: usize) {
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(**self).write_usize(i)
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}
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fn write_i8(&mut self, i: i8) {
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(**self).write_i8(i)
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}
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fn write_i16(&mut self, i: i16) {
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(**self).write_i16(i)
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}
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fn write_i32(&mut self, i: i32) {
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(**self).write_i32(i)
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}
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fn write_i64(&mut self, i: i64) {
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(**self).write_i64(i)
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}
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fn write_i128(&mut self, i: i128) {
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(**self).write_i128(i)
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}
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fn write_isize(&mut self, i: isize) {
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(**self).write_isize(i)
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}
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}
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impl<'a, T: ?Sized> From<Box<'a, T>> for Pin<Box<'a, T>> {
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/// Converts a `Box<T>` into a `Pin<Box<T>>`.
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///
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/// This conversion does not allocate on the heap and happens in place.
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fn from(boxed: Box<'a, T>) -> Self {
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// It's not possible to move or replace the insides of a `Pin<Box<T>>`
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// when `T: !Unpin`, so it's safe to pin it directly without any
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// additional requirements.
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unsafe { Pin::new_unchecked(boxed) }
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}
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}
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impl<'a> Box<'a, dyn Any> {
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#[inline]
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/// Attempt to downcast the box to a concrete type.
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///
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/// # Examples
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///
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/// ```
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/// use std::any::Any;
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///
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/// fn print_if_string(value: Box<dyn Any>) {
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/// if let Ok(string) = value.downcast::<String>() {
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/// println!("String ({}): {}", string.len(), string);
|
|
/// }
|
|
/// }
|
|
///
|
|
/// let my_string = "Hello World".to_string();
|
|
/// print_if_string(Box::new(my_string));
|
|
/// print_if_string(Box::new(0i8));
|
|
/// ```
|
|
pub fn downcast<T: Any>(self) -> Result<Box<'a, T>, Box<'a, dyn Any>> {
|
|
if self.is::<T>() {
|
|
unsafe {
|
|
let raw: *mut dyn Any = Box::into_raw(self);
|
|
Ok(Box::from_raw(raw as *mut T))
|
|
}
|
|
} else {
|
|
Err(self)
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<'a> Box<'a, dyn Any + Send> {
|
|
#[inline]
|
|
/// Attempt to downcast the box to a concrete type.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::any::Any;
|
|
///
|
|
/// fn print_if_string(value: Box<dyn Any + Send>) {
|
|
/// if let Ok(string) = value.downcast::<String>() {
|
|
/// println!("String ({}): {}", string.len(), string);
|
|
/// }
|
|
/// }
|
|
///
|
|
/// let my_string = "Hello World".to_string();
|
|
/// print_if_string(Box::new(my_string));
|
|
/// print_if_string(Box::new(0i8));
|
|
/// ```
|
|
pub fn downcast<T: Any>(self) -> Result<Box<'a, T>, Box<'a, dyn Any + Send>> {
|
|
if self.is::<T>() {
|
|
unsafe {
|
|
let raw: *mut (dyn Any + Send) = Box::into_raw(self);
|
|
Ok(Box::from_raw(raw as *mut T))
|
|
}
|
|
} else {
|
|
Err(self)
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<'a, T: fmt::Display + ?Sized> fmt::Display for Box<'a, T> {
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
|
fmt::Display::fmt(&**self, f)
|
|
}
|
|
}
|
|
|
|
impl<'a, T: fmt::Debug + ?Sized> fmt::Debug for Box<'a, T> {
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
|
fmt::Debug::fmt(&**self, f)
|
|
}
|
|
}
|
|
|
|
impl<'a, T: ?Sized> fmt::Pointer for Box<'a, T> {
|
|
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)
|
|
}
|
|
}
|
|
|
|
impl<'a, T: ?Sized> Deref for Box<'a, T> {
|
|
type Target = T;
|
|
|
|
fn deref(&self) -> &T {
|
|
&*self.0
|
|
}
|
|
}
|
|
|
|
impl<'a, T: ?Sized> DerefMut for Box<'a, T> {
|
|
fn deref_mut(&mut self) -> &mut T {
|
|
self.0
|
|
}
|
|
}
|
|
|
|
impl<'a, I: Iterator + ?Sized> Iterator for Box<'a, I> {
|
|
type Item = I::Item;
|
|
fn next(&mut self) -> Option<I::Item> {
|
|
(**self).next()
|
|
}
|
|
fn size_hint(&self) -> (usize, Option<usize>) {
|
|
(**self).size_hint()
|
|
}
|
|
fn nth(&mut self, n: usize) -> Option<I::Item> {
|
|
(**self).nth(n)
|
|
}
|
|
fn last(self) -> Option<I::Item> {
|
|
#[inline]
|
|
fn some<T>(_: Option<T>, x: T) -> Option<T> {
|
|
Some(x)
|
|
}
|
|
self.fold(None, some)
|
|
}
|
|
}
|
|
|
|
impl<'a, I: DoubleEndedIterator + ?Sized> DoubleEndedIterator for Box<'a, I> {
|
|
fn next_back(&mut self) -> Option<I::Item> {
|
|
(**self).next_back()
|
|
}
|
|
fn nth_back(&mut self, n: usize) -> Option<I::Item> {
|
|
(**self).nth_back(n)
|
|
}
|
|
}
|
|
impl<'a, I: ExactSizeIterator + ?Sized> ExactSizeIterator for Box<'a, I> {
|
|
fn len(&self) -> usize {
|
|
(**self).len()
|
|
}
|
|
}
|
|
|
|
impl<'a, I: FusedIterator + ?Sized> FusedIterator for Box<'a, I> {}
|
|
|
|
#[cfg(feature = "collections")]
|
|
impl<'a, A> Box<'a, [A]> {
|
|
/// Creates a value from an iterator.
|
|
/// This method is an adapted version of [`FromIterator::from_iter`][from_iter].
|
|
/// It cannot be made as that trait implementation given different signature.
|
|
///
|
|
/// [from_iter]: https://doc.rust-lang.org/std/iter/trait.FromIterator.html#tymethod.from_iter
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Basic usage:
|
|
/// ```
|
|
/// use bumpalo::{Bump, boxed::Box, vec};
|
|
///
|
|
/// let b = Bump::new();
|
|
///
|
|
/// let five_fives = std::iter::repeat(5).take(5);
|
|
/// let slice = Box::from_iter_in(five_fives, &b);
|
|
/// assert_eq!(vec![in &b; 5, 5, 5, 5, 5], &*slice);
|
|
/// ```
|
|
pub fn from_iter_in<T: IntoIterator<Item = A>>(iter: T, a: &'a Bump) -> Self {
|
|
use crate::collections::Vec;
|
|
let mut vec = Vec::new_in(a);
|
|
vec.extend(iter);
|
|
vec.into_boxed_slice()
|
|
}
|
|
}
|
|
|
|
impl<'a, T: ?Sized> borrow::Borrow<T> for Box<'a, T> {
|
|
fn borrow(&self) -> &T {
|
|
&**self
|
|
}
|
|
}
|
|
|
|
impl<'a, T: ?Sized> borrow::BorrowMut<T> for Box<'a, T> {
|
|
fn borrow_mut(&mut self) -> &mut T {
|
|
&mut **self
|
|
}
|
|
}
|
|
|
|
impl<'a, T: ?Sized> AsRef<T> for Box<'a, T> {
|
|
fn as_ref(&self) -> &T {
|
|
&**self
|
|
}
|
|
}
|
|
|
|
impl<'a, T: ?Sized> AsMut<T> for Box<'a, T> {
|
|
fn as_mut(&mut self) -> &mut T {
|
|
&mut **self
|
|
}
|
|
}
|
|
|
|
impl<'a, T: ?Sized> Unpin for Box<'a, T> {}
|
|
|
|
impl<'a, F: ?Sized + Future + Unpin> Future for Box<'a, F> {
|
|
type Output = F::Output;
|
|
|
|
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
|
|
F::poll(Pin::new(&mut *self), cx)
|
|
}
|
|
}
|
|
|
|
/// This impl replaces unsize coercion.
|
|
impl<'a, T, const N: usize> From<Box<'a, [T; N]>> for Box<'a, [T]> {
|
|
fn from(mut arr: Box<'a, [T; N]>) -> Box<'a, [T]> {
|
|
let ptr = core::ptr::slice_from_raw_parts_mut(arr.as_mut_ptr(), N);
|
|
mem::forget(arr);
|
|
unsafe { Box::from_raw(ptr) }
|
|
}
|
|
}
|
|
|
|
/// This impl replaces unsize coercion.
|
|
impl<'a, T, const N: usize> TryFrom<Box<'a, [T]>> for Box<'a, [T; N]> {
|
|
type Error = Box<'a, [T]>;
|
|
fn try_from(mut slice: Box<'a, [T]>) -> Result<Box<'a, [T; N]>, Box<'a, [T]>> {
|
|
if slice.len() == N {
|
|
let ptr = slice.as_mut_ptr() as *mut [T; N];
|
|
mem::forget(slice);
|
|
Ok(unsafe { Box::from_raw(ptr) })
|
|
} else {
|
|
Err(slice)
|
|
}
|
|
}
|
|
}
|