| // 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::{BoxPlace, Boxed, InPlace, Place, Placer}; |
| 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. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Box::new(5); |
| /// let ptr = Box::into_raw(x); |
| /// let x = unsafe { Box::from_raw(ptr) }; |
| /// ``` |
| #[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 x = Box::new(5); |
| /// let ptr = Box::into_raw(x); |
| /// ``` |
| #[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. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn print_if_string(value: Box<Any>) { |
| /// if let Ok(string) = value.downcast::<String>() { |
| /// println!("String ({}): {}", string.len(), string); |
| /// } |
| /// } |
| /// |
| /// fn main() { |
| /// 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<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. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn print_if_string(value: Box<Any + Send>) { |
| /// if let Ok(string) = value.downcast::<String>() { |
| /// println!("String ({}): {}", string.len(), string); |
| /// } |
| /// } |
| /// |
| /// fn main() { |
| /// 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<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 = "will be deprecated if and when Box<FnOnce> becomes usable", issue = "28796")] |
| pub trait FnBox<A> { |
| type Output; |
| |
| fn call_box(self: Box<Self>, args: A) -> Self::Output; |
| } |
| |
| #[unstable(feature = "fnbox", |
| reason = "will be deprecated if and when Box<FnOnce> becomes usable", 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 = "will be deprecated if and when Box<FnOnce> becomes usable", 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 = "will be deprecated if and when Box<FnOnce> becomes usable", 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 |
| } |
| } |