Source code
Revision control
Copy as Markdown
Other Tools
//! 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.
//!
//! [`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
//! [`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::ManuallyDrop,
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 mut b = ManuallyDrop::new(b);
b.deref_mut().0 as *mut T
}
/// 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.
///
///
/// # 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(arr: Box<'a, [T; N]>) -> Box<'a, [T]> {
let mut arr = ManuallyDrop::new(arr);
let ptr = core::ptr::slice_from_raw_parts_mut(arr.as_mut_ptr(), N);
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(slice: Box<'a, [T]>) -> Result<Box<'a, [T; N]>, Box<'a, [T]>> {
if slice.len() == N {
let mut slice = ManuallyDrop::new(slice);
let ptr = slice.as_mut_ptr() as *mut [T; N];
Ok(unsafe { Box::from_raw(ptr) })
} else {
Err(slice)
}
}
}