liballoc

1 files changed, 643 insertions, 0 deletions

diff --git a/liballoc/boxed.rs b/liballoc/boxed.rs
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+// Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! A pointer type for heap allocation.
+//!
+//! `Box<T>`, casually referred to as a 'box', provides the simplest form of
+//! heap allocation in Rust. Boxes provide ownership for this allocation, and
+//! drop their contents when they go out of scope.
+//!
+//! # Examples
+//!
+//! Creating a box:
+//!
+//! ```
+//! let x = Box::new(5);
+//! ```
+//!
+//! Creating a recursive data structure:
+//!
+//! ```
+//! #[derive(Debug)]
+//! enum List<T> {
+//!     Cons(T, Box<List<T>>),
+//!     Nil,
+//! }
+//!
+//! fn main() {
+//!     let list: List<i32> = List::Cons(1, Box::new(List::Cons(2, Box::new(List::Nil))));
+//!     println!("{:?}", list);
+//! }
+//! ```
+//!
+//! This will print `Cons(1, Cons(2, Nil))`.
+//!
+//! Recursive structures must be boxed, because if the definition of `Cons`
+//! looked like this:
+//!
+//! ```rust,ignore
+//! 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`, which has a defined size, we know how
+//! big `Cons` needs to be.
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+use heap;
+use raw_vec::RawVec;
+
+use core::any::Any;
+use core::borrow;
+use core::cmp::Ordering;
+use core::fmt;
+use core::hash::{self, Hash};
+use core::marker::{self, Unsize};
+use core::mem;
+use core::ops::{CoerceUnsized, Deref, DerefMut};
+use core::ops::{Placer, Boxed, Place, InPlace, BoxPlace};
+use core::ptr::{self, Unique};
+use core::raw::TraitObject;
+use core::convert::From;
+
+/// A value that represents the heap. This is the default place that the `box`
+/// keyword allocates into when no place is supplied.
+///
+/// The following two examples are equivalent:
+///
+/// ```
+/// #![feature(box_heap)]
+///
+/// #![feature(box_syntax, placement_in_syntax)]
+/// use std::boxed::HEAP;
+///
+/// fn main() {
+///     let foo: Box<i32> = in HEAP { 5 };
+///     let foo = box 5;
+/// }
+/// ```
+#[unstable(feature = "box_heap",
+           reason = "may be renamed; uncertain about custom allocator design",
+           issue = "27779")]
+pub const HEAP: ExchangeHeapSingleton = ExchangeHeapSingleton { _force_singleton: () };
+
+/// This the singleton type used solely for `boxed::HEAP`.
+#[unstable(feature = "box_heap",
+           reason = "may be renamed; uncertain about custom allocator design",
+           issue = "27779")]
+#[derive(Copy, Clone)]
+pub struct ExchangeHeapSingleton {
+    _force_singleton: (),
+}
+
+/// A pointer type for heap allocation.
+///
+/// See the [module-level documentation](../../std/boxed/index.html) for more.
+#[lang = "owned_box"]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Box<T: ?Sized>(Unique<T>);
+
+/// `IntermediateBox` represents uninitialized backing storage for `Box`.
+///
+/// FIXME (pnkfelix): Ideally we would just reuse `Box<T>` instead of
+/// introducing a separate `IntermediateBox<T>`; but then you hit
+/// issues when you e.g. attempt to destructure an instance of `Box`,
+/// since it is a lang item and so it gets special handling by the
+/// compiler.  Easier just to make this parallel type for now.
+///
+/// FIXME (pnkfelix): Currently the `box` protocol only supports
+/// creating instances of sized types. This IntermediateBox is
+/// designed to be forward-compatible with a future protocol that
+/// supports creating instances of unsized types; that is why the type
+/// parameter has the `?Sized` generalization marker, and is also why
+/// this carries an explicit size. However, it probably does not need
+/// to carry the explicit alignment; that is just a work-around for
+/// the fact that the `align_of` intrinsic currently requires the
+/// input type to be Sized (which I do not think is strictly
+/// necessary).
+#[unstable(feature = "placement_in",
+           reason = "placement box design is still being worked out.",
+           issue = "27779")]
+pub struct IntermediateBox<T: ?Sized> {
+    ptr: *mut u8,
+    size: usize,
+    align: usize,
+    marker: marker::PhantomData<*mut T>,
+}
+
+#[unstable(feature = "placement_in",
+           reason = "placement box design is still being worked out.",
+           issue = "27779")]
+impl<T> Place<T> for IntermediateBox<T> {
+    fn pointer(&mut self) -> *mut T {
+        self.ptr as *mut T
+    }
+}
+
+unsafe fn finalize<T>(b: IntermediateBox<T>) -> Box<T> {
+    let p = b.ptr as *mut T;
+    mem::forget(b);
+    mem::transmute(p)
+}
+
+fn make_place<T>() -> IntermediateBox<T> {
+    let size = mem::size_of::<T>();
+    let align = mem::align_of::<T>();
+
+    let p = if size == 0 {
+        heap::EMPTY as *mut u8
+    } else {
+        let p = unsafe { heap::allocate(size, align) };
+        if p.is_null() {
+            panic!("Box make_place allocation failure.");
+        }
+        p
+    };
+
+    IntermediateBox {
+        ptr: p,
+        size: size,
+        align: align,
+        marker: marker::PhantomData,
+    }
+}
+
+#[unstable(feature = "placement_in",
+           reason = "placement box design is still being worked out.",
+           issue = "27779")]
+impl<T> BoxPlace<T> for IntermediateBox<T> {
+    fn make_place() -> IntermediateBox<T> {
+        make_place()
+    }
+}
+
+#[unstable(feature = "placement_in",
+           reason = "placement box design is still being worked out.",
+           issue = "27779")]
+impl<T> InPlace<T> for IntermediateBox<T> {
+    type Owner = Box<T>;
+    unsafe fn finalize(self) -> Box<T> {
+        finalize(self)
+    }
+}
+
+#[unstable(feature = "placement_new_protocol", issue = "27779")]
+impl<T> Boxed for Box<T> {
+    type Data = T;
+    type Place = IntermediateBox<T>;
+    unsafe fn finalize(b: IntermediateBox<T>) -> Box<T> {
+        finalize(b)
+    }
+}
+
+#[unstable(feature = "placement_in",
+           reason = "placement box design is still being worked out.",
+           issue = "27779")]
+impl<T> Placer<T> for ExchangeHeapSingleton {
+    type Place = IntermediateBox<T>;
+
+    fn make_place(self) -> IntermediateBox<T> {
+        make_place()
+    }
+}
+
+#[unstable(feature = "placement_in",
+           reason = "placement box design is still being worked out.",
+           issue = "27779")]
+impl<T: ?Sized> Drop for IntermediateBox<T> {
+    fn drop(&mut self) {
+        if self.size > 0 {
+            unsafe { heap::deallocate(self.ptr, self.size, self.align) }
+        }
+    }
+}
+
+impl<T> Box<T> {
+    /// Allocates memory on the heap and then places `x` into it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let five = Box::new(5);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline(always)]
+    pub fn new(x: T) -> Box<T> {
+        box x
+    }
+}
+
+impl<T: ?Sized> Box<T> {
+    /// Constructs a box from a raw pointer.
+    ///
+    /// After calling this function, the raw pointer is owned by the
+    /// resulting `Box`. Specifically, the `Box` destructor will call
+    /// the destructor of `T` and free the allocated memory. Since the
+    /// way `Box` allocates and releases memory is unspecified, the
+    /// only valid pointer to pass to this function is the one taken
+    /// from another `Box` via the `Box::into_raw` function.
+    ///
+    /// 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.
+    #[stable(feature = "box_raw", since = "1.4.0")]
+    #[inline]
+    pub unsafe fn from_raw(raw: *mut T) -> Self {
+        mem::transmute(raw)
+    }
+
+    /// Consumes the `Box`, returning the wrapped raw pointer.
+    ///
+    /// After calling this function, the caller is responsible for the
+    /// memory previously managed by the `Box`. In particular, the
+    /// caller should properly destroy `T` and release the memory. The
+    /// proper way to do so is to convert the raw pointer back into a
+    /// `Box` with the `Box::from_raw` function.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let seventeen = Box::new(17);
+    /// let raw = Box::into_raw(seventeen);
+    /// let boxed_again = unsafe { Box::from_raw(raw) };
+    /// ```
+    #[stable(feature = "box_raw", since = "1.4.0")]
+    #[inline]
+    pub fn into_raw(b: Box<T>) -> *mut T {
+        unsafe { mem::transmute(b) }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Default> Default for Box<T> {
+    fn default() -> Box<T> {
+        box Default::default()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Default for Box<[T]> {
+    fn default() -> Box<[T]> {
+        Box::<[T; 0]>::new([])
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Clone> Clone for Box<T> {
+    /// Returns a new box with a `clone()` of this box's contents.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x = Box::new(5);
+    /// let y = x.clone();
+    /// ```
+    #[rustfmt_skip]
+    #[inline]
+    fn clone(&self) -> Box<T> {
+        box { (**self).clone() }
+    }
+    /// Copies `source`'s contents into `self` without creating a new allocation.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x = Box::new(5);
+    /// let mut y = Box::new(10);
+    ///
+    /// y.clone_from(&x);
+    ///
+    /// assert_eq!(*y, 5);
+    /// ```
+    #[inline]
+    fn clone_from(&mut self, source: &Box<T>) {
+        (**self).clone_from(&(**source));
+    }
+}
+
+
+#[stable(feature = "box_slice_clone", since = "1.3.0")]
+impl Clone for Box<str> {
+    fn clone(&self) -> Self {
+        let len = self.len();
+        let buf = RawVec::with_capacity(len);
+        unsafe {
+            ptr::copy_nonoverlapping(self.as_ptr(), buf.ptr(), len);
+            mem::transmute(buf.into_box()) // bytes to str ~magic
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized + PartialEq> PartialEq for Box<T> {
+    #[inline]
+    fn eq(&self, other: &Box<T>) -> bool {
+        PartialEq::eq(&**self, &**other)
+    }
+    #[inline]
+    fn ne(&self, other: &Box<T>) -> bool {
+        PartialEq::ne(&**self, &**other)
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized + PartialOrd> PartialOrd for Box<T> {
+    #[inline]
+    fn partial_cmp(&self, other: &Box<T>) -> Option<Ordering> {
+        PartialOrd::partial_cmp(&**self, &**other)
+    }
+    #[inline]
+    fn lt(&self, other: &Box<T>) -> bool {
+        PartialOrd::lt(&**self, &**other)
+    }
+    #[inline]
+    fn le(&self, other: &Box<T>) -> bool {
+        PartialOrd::le(&**self, &**other)
+    }
+    #[inline]
+    fn ge(&self, other: &Box<T>) -> bool {
+        PartialOrd::ge(&**self, &**other)
+    }
+    #[inline]
+    fn gt(&self, other: &Box<T>) -> bool {
+        PartialOrd::gt(&**self, &**other)
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized + Ord> Ord for Box<T> {
+    #[inline]
+    fn cmp(&self, other: &Box<T>) -> Ordering {
+        Ord::cmp(&**self, &**other)
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized + Eq> Eq for Box<T> {}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized + Hash> Hash for Box<T> {
+    fn hash<H: hash::Hasher>(&self, state: &mut H) {
+        (**self).hash(state);
+    }
+}
+
+#[stable(feature = "from_for_ptrs", since = "1.6.0")]
+impl<T> From<T> for Box<T> {
+    fn from(t: T) -> Self {
+        Box::new(t)
+    }
+}
+
+impl Box<Any> {
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    /// Attempt to downcast the box to a concrete type.
+    pub fn downcast<T: Any>(self) -> Result<Box<T>, Box<Any>> {
+        if self.is::<T>() {
+            unsafe {
+                // Get the raw representation of the trait object
+                let raw = Box::into_raw(self);
+                let to: TraitObject = mem::transmute::<*mut Any, TraitObject>(raw);
+
+                // Extract the data pointer
+                Ok(Box::from_raw(to.data as *mut T))
+            }
+        } else {
+            Err(self)
+        }
+    }
+}
+
+impl Box<Any + Send> {
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    /// Attempt to downcast the box to a concrete type.
+    pub fn downcast<T: Any>(self) -> Result<Box<T>, Box<Any + Send>> {
+        <Box<Any>>::downcast(self).map_err(|s| unsafe {
+            // reapply the Send marker
+            mem::transmute::<Box<Any>, Box<Any + Send>>(s)
+        })
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: fmt::Display + ?Sized> fmt::Display for Box<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: fmt::Debug + ?Sized> fmt::Debug for Box<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> fmt::Pointer for Box<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)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> Deref for Box<T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        &**self
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> DerefMut for Box<T> {
+    fn deref_mut(&mut self) -> &mut T {
+        &mut **self
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<I: Iterator + ?Sized> Iterator for Box<I> {
+    type Item = I::Item;
+    fn next(&mut self) -> Option<I::Item> {
+        (**self).next()
+    }
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (**self).size_hint()
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<I: DoubleEndedIterator + ?Sized> DoubleEndedIterator for Box<I> {
+    fn next_back(&mut self) -> Option<I::Item> {
+        (**self).next_back()
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<I: ExactSizeIterator + ?Sized> ExactSizeIterator for Box<I> {}
+
+
+/// `FnBox` is a version of the `FnOnce` intended for use with boxed
+/// closure objects. The idea is that where one would normally store a
+/// `Box<FnOnce()>` in a data structure, you should use
+/// `Box<FnBox()>`. The two traits behave essentially the same, except
+/// that a `FnBox` closure can only be called if it is boxed. (Note
+/// that `FnBox` may be deprecated in the future if `Box<FnOnce()>`
+/// closures become directly usable.)
+///
+/// ### Example
+///
+/// Here is a snippet of code which creates a hashmap full of boxed
+/// once closures and then removes them one by one, calling each
+/// closure as it is removed. Note that the type of the closures
+/// stored in the map is `Box<FnBox() -> i32>` and not `Box<FnOnce()
+/// -> 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 = "28796")]
+pub trait FnBox<A> {
+    type Output;
+
+    fn call_box(self: Box<Self>, args: A) -> Self::Output;
+}
+
+#[unstable(feature = "fnbox", reason = "Newly introduced", issue = "28796")]
+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)
+    }
+}
+
+#[unstable(feature = "fnbox", reason = "Newly introduced", issue = "28796")]
+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)
+    }
+}
+
+#[unstable(feature = "fnbox", reason = "Newly introduced", issue = "28796")]
+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)
+    }
+}
+
+#[unstable(feature = "coerce_unsized", issue = "27732")]
+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);
+                    }
+                }
+            }
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> borrow::Borrow<T> for Box<T> {
+    fn borrow(&self) -> &T {
+        &**self
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+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
+    }
+}