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Diffstat (limited to 'third_party/rust/bumpalo/src/boxed.rs')
| -rw-r--r-- | third_party/rust/bumpalo/src/boxed.rs | 684 |
1 files changed, 684 insertions, 0 deletions
diff --git a/third_party/rust/bumpalo/src/boxed.rs b/third_party/rust/bumpalo/src/boxed.rs new file mode 100644 index 0000000000..cf9f4d6fee --- /dev/null +++ b/third_party/rust/bumpalo/src/boxed.rs @@ -0,0 +1,684 @@ +//! A pointer type for bump allocation. +//! +//! [`Box<'a, T>`] provides the simplest form of +//! bump allocation in `bumpalo`. Boxes provide ownership for this allocation, and +//! drop their contents when they go out of scope. +//! +//! # Examples +//! +//! Move a value from the stack to the heap by creating a [`Box`]: +//! +//! ``` +//! use bumpalo::{Bump, boxed::Box}; +//! +//! let b = Bump::new(); +//! +//! let val: u8 = 5; +//! let boxed: Box<u8> = Box::new_in(val, &b); +//! ``` +//! +//! Move a value from a [`Box`] back to the stack by [dereferencing]: +//! +//! ``` +//! use bumpalo::{Bump, boxed::Box}; +//! +//! let b = Bump::new(); +//! +//! let boxed: Box<u8> = Box::new_in(5, &b); +//! let val: u8 = *boxed; +//! ``` +//! +//! Running [`Drop`] implementations on bump-allocated values: +//! +//! ``` +//! use bumpalo::{Bump, boxed::Box}; +//! use std::sync::atomic::{AtomicUsize, Ordering}; +//! +//! static NUM_DROPPED: AtomicUsize = AtomicUsize::new(0); +//! +//! struct CountDrops; +//! +//! impl Drop for CountDrops { +//! fn drop(&mut self) { +//! NUM_DROPPED.fetch_add(1, Ordering::SeqCst); +//! } +//! } +//! +//! // Create a new bump arena. +//! let bump = Bump::new(); +//! +//! // Create a `CountDrops` inside the bump arena. +//! let mut c = Box::new_in(CountDrops, &bump); +//! +//! // No `CountDrops` have been dropped yet. +//! assert_eq!(NUM_DROPPED.load(Ordering::SeqCst), 0); +//! +//! // Drop our `Box<CountDrops>`. +//! drop(c); +//! +//! // Its `Drop` implementation was run, and so `NUM_DROPS` has been incremented. +//! assert_eq!(NUM_DROPPED.load(Ordering::SeqCst), 1); +//! ``` +//! +//! Creating a recursive data structure: +//! +//! ``` +//! use bumpalo::{Bump, boxed::Box}; +//! +//! let b = Bump::new(); +//! +//! #[derive(Debug)] +//! enum List<'a, T> { +//! Cons(T, Box<'a, List<'a, T>>), +//! Nil, +//! } +//! +//! let list: List<i32> = List::Cons(1, Box::new_in(List::Cons(2, Box::new_in(List::Nil, &b)), &b)); +//! println!("{:?}", list); +//! ``` +//! +//! This will print `Cons(1, Cons(2, Nil))`. +//! +//! Recursive structures must be boxed, because if the definition of `Cons` +//! looked like this: +//! +//! ```compile_fail,E0072 +//! # enum List<T> { +//! Cons(T, List<T>), +//! # } +//! ``` +//! +//! It wouldn't work. This is because the size of a `List` depends on how many +//! elements are in the list, and so we don't know how much memory to allocate +//! for a `Cons`. By introducing a [`Box<'a, T>`], which has a defined size, we know how +//! big `Cons` needs to be. +//! +//! # Memory layout +//! +//! For non-zero-sized values, a [`Box`] will use the provided [`Bump`] allocator for +//! its allocation. It is valid to convert both ways between a [`Box`] and a +//! pointer allocated with the [`Bump`] allocator, given that the +//! [`Layout`] used with the allocator is correct for the type. More precisely, +//! a `value: *mut T` that has been allocated with the [`Bump`] allocator +//! with `Layout::for_value(&*value)` may be converted into a box using +//! [`Box::<T>::from_raw(value)`]. Conversely, the memory backing a `value: *mut +//! T` obtained from [`Box::<T>::into_raw`] will be deallocated by the +//! [`Bump`] allocator with [`Layout::for_value(&*value)`]. +//! +//! Note that roundtrip `Box::from_raw(Box::into_raw(b))` looses the lifetime bound to the +//! [`Bump`] immutable borrow which guarantees that the allocator will not be reset +//! and memory will not be freed. +//! +//! [dereferencing]: https://doc.rust-lang.org/std/ops/trait.Deref.html +//! [`Box`]: struct.Box.html +//! [`Box<'a, T>`]: struct.Box.html +//! [`Box::<T>::from_raw(value)`]: struct.Box.html#method.from_raw +//! [`Box::<T>::into_raw`]: struct.Box.html#method.into_raw +//! [`Bump`]: ../struct.Bump.html +//! [`Drop`]: https://doc.rust-lang.org/std/ops/trait.Drop.html +//! [`Layout`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html +//! [`Layout::for_value(&*value)`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.for_value + +use { + crate::Bump, + { + core::{ + any::Any, + borrow, + cmp::Ordering, + convert::TryFrom, + future::Future, + hash::{Hash, Hasher}, + iter::FusedIterator, + mem, + ops::{Deref, DerefMut}, + pin::Pin, + task::{Context, Poll}, + }, + core_alloc::fmt, + }, +}; + +/// An owned pointer to a bump-allocated `T` value, that runs `Drop` +/// implementations. +/// +/// See the [module-level documentation][crate::boxed] for more details. +#[repr(transparent)] +pub struct Box<'a, T: ?Sized>(&'a mut T); + +impl<'a, T> Box<'a, T> { + /// Allocates memory on the heap and then places `x` into it. + /// + /// This doesn't actually allocate if `T` is zero-sized. + /// + /// # Examples + /// + /// ``` + /// use bumpalo::{Bump, boxed::Box}; + /// + /// let b = Bump::new(); + /// + /// let five = Box::new_in(5, &b); + /// ``` + #[inline(always)] + pub fn new_in(x: T, a: &'a Bump) -> Box<'a, T> { + Box(a.alloc(x)) + } + + /// Constructs a new `Pin<Box<T>>`. If `T` does not implement `Unpin`, then + /// `x` will be pinned in memory and unable to be moved. + #[inline(always)] + pub fn pin_in(x: T, a: &'a Bump) -> Pin<Box<'a, T>> { + Box(a.alloc(x)).into() + } + + /// Consumes the `Box`, returning the wrapped value. + /// + /// # Examples + /// + /// ``` + /// use bumpalo::{Bump, boxed::Box}; + /// + /// let b = Bump::new(); + /// + /// let hello = Box::new_in("hello".to_owned(), &b); + /// assert_eq!(Box::into_inner(hello), "hello"); + /// ``` + pub fn into_inner(b: Box<'a, T>) -> T { + // `Box::into_raw` returns a pointer that is properly aligned and non-null. + // The underlying `Bump` only frees the memory, but won't call the destructor. + unsafe { core::ptr::read(Box::into_raw(b)) } + } +} + +impl<'a, T: ?Sized> Box<'a, 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. + /// + /// # Examples + /// + /// Recreate a `Box` which was previously converted to a raw pointer + /// using [`Box::into_raw`]: + /// ``` + /// use bumpalo::{Bump, boxed::Box}; + /// + /// let b = Bump::new(); + /// + /// let x = Box::new_in(5, &b); + /// let ptr = Box::into_raw(x); + /// 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. + /// ``` + /// Manually create a `Box` from scratch by using the bump allocator: + /// ``` + /// use std::alloc::{alloc, Layout}; + /// use bumpalo::{Bump, boxed::Box}; + /// + /// let b = Bump::new(); + /// + /// unsafe { + /// let ptr = b.alloc_layout(Layout::new::<i32>()).as_ptr() as *mut i32; + /// *ptr = 5; + /// 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. + /// } + /// ``` + #[inline] + pub unsafe fn from_raw(raw: *mut T) -> Self { + Box(&mut *raw) + } + + /// 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 + /// value previously managed by the `Box`. In particular, the + /// caller should properly destroy `T`. 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: + /// ``` + /// use bumpalo::{Bump, boxed::Box}; + /// + /// let b = Bump::new(); + /// + /// let x = Box::new_in(String::from("Hello"), &b); + /// let ptr = Box::into_raw(x); + /// 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. + /// ``` + /// Manual cleanup by explicitly running the destructor: + /// ``` + /// use std::ptr; + /// use bumpalo::{Bump, boxed::Box}; + /// + /// let b = Bump::new(); + /// + /// let mut x = Box::new_in(String::from("Hello"), &b); + /// let p = Box::into_raw(x); + /// unsafe { + /// ptr::drop_in_place(p); + /// } + /// ``` + #[inline] + pub fn into_raw(b: Box<'a, T>) -> *mut T { + let ptr = b.0 as *mut T; + mem::forget(b); + ptr + } + + /// 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: + /// + /// ``` + /// use bumpalo::{Bump, boxed::Box}; + /// + /// let b = Bump::new(); + /// + /// let x = Box::new_in(41, &b); + /// let reference: &mut usize = Box::leak(x); + /// *reference += 1; + /// assert_eq!(*reference, 42); + /// ``` + /// + ///``` + /// # #[cfg(feature = "collections")] + /// # { + /// use bumpalo::{Bump, boxed::Box, vec}; + /// + /// let b = Bump::new(); + /// + /// let x = vec![in &b; 1, 2, 3].into_boxed_slice(); + /// let reference = Box::leak(x); + /// reference[0] = 4; + /// assert_eq!(*reference, [4, 2, 3]); + /// # } + ///``` + #[inline] + pub fn leak(b: Box<'a, T>) -> &'a mut T { + unsafe { &mut *Box::into_raw(b) } + } +} + +impl<'a, T: ?Sized> Drop for Box<'a, T> { + fn drop(&mut self) { + unsafe { + // `Box` owns value of `T`, but not memory behind it. + core::ptr::drop_in_place(self.0); + } + } +} + +impl<'a, T> Default for Box<'a, [T]> { + fn default() -> Box<'a, [T]> { + // It should be OK to `drop_in_place` empty slice of anything. + Box(&mut []) + } +} + +impl<'a> Default for Box<'a, str> { + fn default() -> Box<'a, str> { + // Empty slice is valid string. + // It should be OK to `drop_in_place` empty str. + unsafe { Box::from_raw(Box::into_raw(Box::<[u8]>::default()) as *mut str) } + } +} + +impl<'a, 'b, T: ?Sized + PartialEq> PartialEq<Box<'b, T>> for Box<'a, T> { + #[inline] + fn eq(&self, other: &Box<'b, T>) -> bool { + PartialEq::eq(&**self, &**other) + } + #[inline] + fn ne(&self, other: &Box<'b, T>) -> bool { + PartialEq::ne(&**self, &**other) + } +} + +impl<'a, 'b, T: ?Sized + PartialOrd> PartialOrd<Box<'b, T>> for Box<'a, T> { + #[inline] + fn partial_cmp(&self, other: &Box<'b, T>) -> Option<Ordering> { + PartialOrd::partial_cmp(&**self, &**other) + } + #[inline] + fn lt(&self, other: &Box<'b, T>) -> bool { + PartialOrd::lt(&**self, &**other) + } + #[inline] + fn le(&self, other: &Box<'b, T>) -> bool { + PartialOrd::le(&**self, &**other) + } + #[inline] + fn ge(&self, other: &Box<'b, T>) -> bool { + PartialOrd::ge(&**self, &**other) + } + #[inline] + fn gt(&self, other: &Box<'b, T>) -> bool { + PartialOrd::gt(&**self, &**other) + } +} + +impl<'a, T: ?Sized + Ord> Ord for Box<'a, T> { + #[inline] + fn cmp(&self, other: &Box<'a, T>) -> Ordering { + Ord::cmp(&**self, &**other) + } +} + +impl<'a, T: ?Sized + Eq> Eq for Box<'a, T> {} + +impl<'a, T: ?Sized + Hash> Hash for Box<'a, T> { + fn hash<H: Hasher>(&self, state: &mut H) { + (**self).hash(state); + } +} + +impl<'a, T: ?Sized + Hasher> Hasher for Box<'a, T> { + 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) + } +} + +impl<'a, T: ?Sized> From<Box<'a, T>> for Pin<Box<'a, T>> { + /// Converts a `Box<T>` into a `Pin<Box<T>>`. + /// + /// This conversion does not allocate on the heap and happens in place. + fn from(boxed: Box<'a, T>) -> Self { + // 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) } + } +} + +impl<'a> Box<'a, dyn Any> { + #[inline] + /// Attempt to downcast the box to a concrete type. + /// + /// # Examples + /// + /// ``` + /// use std::any::Any; + /// + /// fn print_if_string(value: Box<dyn Any>) { + /// if let Ok(string) = value.downcast::<String>() { + /// println!("String ({}): {}", string.len(), string); + /// } + /// } + /// + /// let my_string = "Hello World".to_string(); + /// print_if_string(Box::new(my_string)); + /// print_if_string(Box::new(0i8)); + /// ``` + 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) + } + } +} |