99093b79f1
Sometimes when writing generic code you want to abstract over
owning/pointer type so that calling code isn't restricted by one
concrete owning/pointer type. This commit makes possible such code:
```rust
fn i_will_work_with_arc<T: Into<Arc<MyTy>>>(t: T) {
let the_arc = t.into();
// Do something
}
i_will_work_with_arc(MyTy::new());
i_will_work_with_arc(Box::new(MyTy::new()));
let arc_that_i_already_have = Arc::new(MyTy::new());
i_will_work_with_arc(arc_that_i_already_have);
```
Please note that this patch doesn't work with DSTs.
Also to mention, I made those impls stable, and I don't know whether they should be actually stable from the beginning. Please tell me if this should be feature-gated.
625 lines
17 KiB
Rust
625 lines
17 KiB
Rust
// Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! A pointer 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.
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//!
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//! # Examples
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//!
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//! Creating a box:
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//!
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//! ```
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//! let x = Box::new(5);
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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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//! #[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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//! fn main() {
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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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//!
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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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//! ```rust,ignore
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//! Cons(T, List<T>),
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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`, which has a defined size, we know how
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//! big `Cons` needs to be.
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#![stable(feature = "rust1", since = "1.0.0")]
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use heap;
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use raw_vec::RawVec;
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use core::any::Any;
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use core::borrow;
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use core::cmp::Ordering;
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use core::fmt;
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use core::hash::{self, Hash};
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use core::marker::{self, Unsize};
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use core::mem;
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use core::ops::{CoerceUnsized, Deref, DerefMut};
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use core::ops::{Placer, Boxed, Place, InPlace, BoxPlace};
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use core::ptr::{self, Unique};
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use core::raw::TraitObject;
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use core::convert::From;
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/// A value that represents the heap. This is the default place that the `box`
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/// keyword allocates into when no place is supplied.
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///
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/// The following two examples are equivalent:
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///
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/// ```
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/// #![feature(box_heap)]
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///
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/// #![feature(box_syntax, placement_in_syntax)]
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/// use std::boxed::HEAP;
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///
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/// fn main() {
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/// let foo: Box<i32> = in HEAP { 5 };
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/// let foo = box 5;
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/// }
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/// ```
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#[unstable(feature = "box_heap",
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reason = "may be renamed; uncertain about custom allocator design",
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issue = "27779")]
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pub const HEAP: ExchangeHeapSingleton =
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ExchangeHeapSingleton { _force_singleton: () };
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/// This the singleton type used solely for `boxed::HEAP`.
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#[unstable(feature = "box_heap",
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reason = "may be renamed; uncertain about custom allocator design",
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issue = "27779")]
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#[derive(Copy, Clone)]
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pub struct ExchangeHeapSingleton {
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_force_singleton: (),
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}
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/// A pointer type for heap allocation.
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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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#[stable(feature = "rust1", since = "1.0.0")]
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#[fundamental]
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pub struct Box<T: ?Sized>(Unique<T>);
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/// `IntermediateBox` represents uninitialized backing storage for `Box`.
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///
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/// FIXME (pnkfelix): Ideally we would just reuse `Box<T>` instead of
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/// introducing a separate `IntermediateBox<T>`; but then you hit
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/// issues when you e.g. attempt to destructure an instance of `Box`,
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/// since it is a lang item and so it gets special handling by the
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/// compiler. Easier just to make this parallel type for now.
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///
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/// FIXME (pnkfelix): Currently the `box` protocol only supports
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/// creating instances of sized types. This IntermediateBox is
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/// designed to be forward-compatible with a future protocol that
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/// supports creating instances of unsized types; that is why the type
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/// parameter has the `?Sized` generalization marker, and is also why
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/// this carries an explicit size. However, it probably does not need
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/// to carry the explicit alignment; that is just a work-around for
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/// the fact that the `align_of` intrinsic currently requires the
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/// input type to be Sized (which I do not think is strictly
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/// necessary).
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#[unstable(feature = "placement_in",
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reason = "placement box design is still being worked out.",
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issue = "27779")]
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pub struct IntermediateBox<T: ?Sized> {
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ptr: *mut u8,
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size: usize,
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align: usize,
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marker: marker::PhantomData<*mut T>,
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}
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impl<T> Place<T> for IntermediateBox<T> {
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fn pointer(&mut self) -> *mut T {
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self.ptr as *mut T
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}
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}
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unsafe fn finalize<T>(b: IntermediateBox<T>) -> Box<T> {
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let p = b.ptr as *mut T;
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mem::forget(b);
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mem::transmute(p)
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}
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fn make_place<T>() -> IntermediateBox<T> {
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let size = mem::size_of::<T>();
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let align = mem::align_of::<T>();
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let p = if size == 0 {
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heap::EMPTY as *mut u8
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} else {
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let p = unsafe { heap::allocate(size, align) };
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if p.is_null() {
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panic!("Box make_place allocation failure.");
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}
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p
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};
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IntermediateBox {
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ptr: p,
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size: size,
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align: align,
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marker: marker::PhantomData,
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}
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}
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impl<T> BoxPlace<T> for IntermediateBox<T> {
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fn make_place() -> IntermediateBox<T> {
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make_place()
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}
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}
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impl<T> InPlace<T> for IntermediateBox<T> {
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type Owner = Box<T>;
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unsafe fn finalize(self) -> Box<T> {
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finalize(self)
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}
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}
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impl<T> Boxed for Box<T> {
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type Data = T;
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type Place = IntermediateBox<T>;
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unsafe fn finalize(b: IntermediateBox<T>) -> Box<T> {
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finalize(b)
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}
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}
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impl<T> Placer<T> for ExchangeHeapSingleton {
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type Place = IntermediateBox<T>;
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fn make_place(self) -> IntermediateBox<T> {
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make_place()
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}
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}
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impl<T: ?Sized> Drop for IntermediateBox<T> {
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fn drop(&mut self) {
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if self.size > 0 {
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unsafe { heap::deallocate(self.ptr, self.size, self.align) }
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}
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}
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}
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impl<T> Box<T> {
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/// Allocates memory on the heap and then moves `x` into it.
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///
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/// # Examples
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///
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/// ```
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/// let x = Box::new(5);
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[inline(always)]
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pub fn new(x: T) -> Box<T> {
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box x
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}
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}
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impl<T : ?Sized> Box<T> {
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/// Constructs a box from the raw pointer.
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///
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/// After this function call, pointer is owned by resulting box.
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/// In particular, it means that `Box` destructor calls destructor
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/// of `T` and releases memory. Since the way `Box` allocates and
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/// releases memory is unspecified, the only valid pointer to pass
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/// to this function is the one taken from another `Box` with
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/// `Box::into_raw` function.
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///
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/// Function is unsafe, because improper use of this function may
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/// lead to memory problems like double-free, for example if the
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/// function is called twice on the same raw pointer.
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#[stable(feature = "box_raw", since = "1.4.0")]
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#[inline]
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pub unsafe fn from_raw(raw: *mut T) -> Self {
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mem::transmute(raw)
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}
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/// Consumes the `Box`, returning the wrapped raw pointer.
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///
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/// After call to this function, caller is responsible for the memory
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/// previously managed by `Box`, in particular caller should properly
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/// destroy `T` and release memory. The proper way to do it is to
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/// convert pointer back to `Box` with `Box::from_raw` function, because
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/// `Box` does not specify, how memory is allocated.
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///
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/// # Examples
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///
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/// ```
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/// let seventeen = Box::new(17u32);
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/// let raw = Box::into_raw(seventeen);
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/// let boxed_again = unsafe { Box::from_raw(raw) };
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/// ```
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#[stable(feature = "box_raw", since = "1.4.0")]
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#[inline]
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pub fn into_raw(b: Box<T>) -> *mut T {
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unsafe { mem::transmute(b) }
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: Default> Default for Box<T> {
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fn default() -> Box<T> {
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box Default::default()
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T> Default for Box<[T]> {
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fn default() -> Box<[T]> {
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Box::<[T; 0]>::new([])
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: Clone> Clone for Box<T> {
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/// Returns a new box with a `clone()` of this box's contents.
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///
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/// # Examples
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///
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/// ```
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/// let x = Box::new(5);
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/// let y = x.clone();
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/// ```
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#[rustfmt_skip]
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#[inline]
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fn clone(&self) -> Box<T> {
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box { (**self).clone() }
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}
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/// Copies `source`'s contents into `self` without creating a new allocation.
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///
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/// # Examples
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///
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/// ```
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/// let x = Box::new(5);
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/// let mut y = Box::new(10);
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///
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/// y.clone_from(&x);
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///
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/// assert_eq!(*y, 5);
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/// ```
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#[inline]
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fn clone_from(&mut self, source: &Box<T>) {
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(**self).clone_from(&(**source));
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}
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}
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#[stable(feature = "box_slice_clone", since = "1.3.0")]
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impl Clone for Box<str> {
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fn clone(&self) -> Self {
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let len = self.len();
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let buf = RawVec::with_capacity(len);
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unsafe {
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ptr::copy_nonoverlapping(self.as_ptr(), buf.ptr(), len);
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mem::transmute(buf.into_box()) // bytes to str ~magic
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}
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: ?Sized + PartialEq> PartialEq for Box<T> {
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#[inline]
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fn eq(&self, other: &Box<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<T>) -> bool {
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PartialEq::ne(&**self, &**other)
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: ?Sized + PartialOrd> PartialOrd for Box<T> {
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#[inline]
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fn partial_cmp(&self, other: &Box<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<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<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<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<T>) -> bool {
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PartialOrd::gt(&**self, &**other)
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: ?Sized + Ord> Ord for Box<T> {
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#[inline]
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fn cmp(&self, other: &Box<T>) -> Ordering {
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Ord::cmp(&**self, &**other)
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: ?Sized + Eq> Eq for Box<T> {}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: ?Sized + Hash> Hash for Box<T> {
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fn hash<H: hash::Hasher>(&self, state: &mut H) {
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(**self).hash(state);
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}
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}
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#[stable(feature = "from_for_ptrs", since = "1.6.0")]
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impl<T> From<T> for Box<T> {
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fn from(t: T) -> Self {
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Box::new(t)
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}
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}
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impl Box<Any> {
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#[inline]
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#[stable(feature = "rust1", since = "1.0.0")]
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/// Attempt to downcast the box to a concrete type.
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pub fn downcast<T: Any>(self) -> Result<Box<T>, Box<Any>> {
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if self.is::<T>() {
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unsafe {
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// Get the raw representation of the trait object
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let raw = Box::into_raw(self);
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let to: TraitObject = mem::transmute::<*mut Any, TraitObject>(raw);
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// Extract the data pointer
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Ok(Box::from_raw(to.data as *mut T))
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}
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} else {
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Err(self)
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}
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}
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}
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impl Box<Any + Send> {
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#[inline]
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#[stable(feature = "rust1", since = "1.0.0")]
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/// Attempt to downcast the box to a concrete type.
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pub fn downcast<T: Any>(self) -> Result<Box<T>, Box<Any + Send>> {
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<Box<Any>>::downcast(self).map_err(|s| unsafe {
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// reapply the Send marker
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mem::transmute::<Box<Any>, Box<Any + Send>>(s)
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})
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: fmt::Display + ?Sized> fmt::Display for Box<T> {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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fmt::Display::fmt(&**self, f)
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: fmt::Debug + ?Sized> fmt::Debug for Box<T> {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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fmt::Debug::fmt(&**self, f)
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T> fmt::Pointer for Box<T> {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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// It's not possible to extract the inner Uniq directly from the Box,
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// instead we cast it to a *const which aliases the Unique
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let ptr: *const T = &**self;
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fmt::Pointer::fmt(&ptr, f)
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: ?Sized> Deref for Box<T> {
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type Target = T;
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fn deref(&self) -> &T {
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&**self
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: ?Sized> DerefMut for Box<T> {
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fn deref_mut(&mut self) -> &mut T {
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&mut **self
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<I: Iterator + ?Sized> Iterator for Box<I> {
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type Item = I::Item;
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fn next(&mut self) -> Option<I::Item> {
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(**self).next()
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}
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fn size_hint(&self) -> (usize, Option<usize>) {
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(**self).size_hint()
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<I: DoubleEndedIterator + ?Sized> DoubleEndedIterator for Box<I> {
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fn next_back(&mut self) -> Option<I::Item> {
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(**self).next_back()
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<I: ExactSizeIterator + ?Sized> ExactSizeIterator for Box<I> {}
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/// `FnBox` is a version of the `FnOnce` intended for use with boxed
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/// closure objects. The idea is that where one would normally store a
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/// `Box<FnOnce()>` in a data structure, you should use
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/// `Box<FnBox()>`. The two traits behave essentially the same, except
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/// that a `FnBox` closure can only be called if it is boxed. (Note
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/// that `FnBox` may be deprecated in the future if `Box<FnOnce()>`
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/// closures become directly usable.)
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///
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/// ### Example
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///
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|
/// Here is a snippet of code which creates a hashmap full of boxed
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/// once closures and then removes them one by one, calling each
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/// closure as it is removed. Note that the type of the closures
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/// stored in the map is `Box<FnBox() -> i32>` and not `Box<FnOnce()
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|
/// -> i32>`.
|
|
///
|
|
/// ```
|
|
/// #![feature(fnbox)]
|
|
///
|
|
/// use std::boxed::FnBox;
|
|
/// use std::collections::HashMap;
|
|
///
|
|
/// fn make_map() -> HashMap<i32, Box<FnBox() -> i32>> {
|
|
/// let mut map: HashMap<i32, Box<FnBox() -> i32>> = HashMap::new();
|
|
/// map.insert(1, Box::new(|| 22));
|
|
/// map.insert(2, Box::new(|| 44));
|
|
/// map
|
|
/// }
|
|
///
|
|
/// fn main() {
|
|
/// let mut map = make_map();
|
|
/// for i in &[1, 2] {
|
|
/// let f = map.remove(&i).unwrap();
|
|
/// assert_eq!(f(), i * 22);
|
|
/// }
|
|
/// }
|
|
/// ```
|
|
#[rustc_paren_sugar]
|
|
#[unstable(feature = "fnbox", reason = "Newly introduced", issue = "0")]
|
|
pub trait FnBox<A> {
|
|
type Output;
|
|
|
|
fn call_box(self: Box<Self>, args: A) -> Self::Output;
|
|
}
|
|
|
|
impl<A,F> FnBox<A> for F
|
|
where F: FnOnce<A>
|
|
{
|
|
type Output = F::Output;
|
|
|
|
fn call_box(self: Box<F>, args: A) -> F::Output {
|
|
self.call_once(args)
|
|
}
|
|
}
|
|
|
|
impl<'a,A,R> FnOnce<A> for Box<FnBox<A,Output=R>+'a> {
|
|
type Output = R;
|
|
|
|
extern "rust-call" fn call_once(self, args: A) -> R {
|
|
self.call_box(args)
|
|
}
|
|
}
|
|
|
|
impl<'a,A,R> FnOnce<A> for Box<FnBox<A,Output=R>+Send+'a> {
|
|
type Output = R;
|
|
|
|
extern "rust-call" fn call_once(self, args: A) -> R {
|
|
self.call_box(args)
|
|
}
|
|
}
|
|
|
|
impl<T: ?Sized+Unsize<U>, U: ?Sized> CoerceUnsized<Box<U>> for Box<T> {}
|
|
|
|
#[stable(feature = "box_slice_clone", since = "1.3.0")]
|
|
impl<T: Clone> Clone for Box<[T]> {
|
|
fn clone(&self) -> Self {
|
|
let mut new = BoxBuilder {
|
|
data: RawVec::with_capacity(self.len()),
|
|
len: 0,
|
|
};
|
|
|
|
let mut target = new.data.ptr();
|
|
|
|
for item in self.iter() {
|
|
unsafe {
|
|
ptr::write(target, item.clone());
|
|
target = target.offset(1);
|
|
};
|
|
|
|
new.len += 1;
|
|
}
|
|
|
|
return unsafe { new.into_box() };
|
|
|
|
// Helper type for responding to panics correctly.
|
|
struct BoxBuilder<T> {
|
|
data: RawVec<T>,
|
|
len: usize,
|
|
}
|
|
|
|
impl<T> BoxBuilder<T> {
|
|
unsafe fn into_box(self) -> Box<[T]> {
|
|
let raw = ptr::read(&self.data);
|
|
mem::forget(self);
|
|
raw.into_box()
|
|
}
|
|
}
|
|
|
|
impl<T> Drop for BoxBuilder<T> {
|
|
fn drop(&mut self) {
|
|
let mut data = self.data.ptr();
|
|
let max = unsafe { data.offset(self.len as isize) };
|
|
|
|
while data != max {
|
|
unsafe {
|
|
ptr::read(data);
|
|
data = data.offset(1);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T: ?Sized> borrow::Borrow<T> for Box<T> {
|
|
fn borrow(&self) -> &T {
|
|
&**self
|
|
}
|
|
}
|
|
|
|
impl<T: ?Sized> borrow::BorrowMut<T> for Box<T> {
|
|
fn borrow_mut(&mut self) -> &mut T {
|
|
&mut **self
|
|
}
|
|
}
|
|
|
|
#[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
|
|
impl<T: ?Sized> AsRef<T> for Box<T> {
|
|
fn as_ref(&self) -> &T {
|
|
&**self
|
|
}
|
|
}
|
|
|
|
#[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
|
|
impl<T: ?Sized> AsMut<T> for Box<T> {
|
|
fn as_mut(&mut self) -> &mut T {
|
|
&mut **self
|
|
}
|
|
}
|