src/libcore/mem.rs - third_party/rust - Git at Google

 // Copyright 2012-2014 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.

 //! Basic functions for dealing with memory.
 //!
 //! This module contains functions for querying the size and alignment of
 //! types, initializing and manipulating memory.

 #![stable(feature = "rust1", since = "1.0.0")]

 use marker::Sized;
 use intrinsics;
 use ptr;

 #[stable(feature = "rust1", since = "1.0.0")]
 pub use intrinsics::transmute;

 /// Leaks a value into the void, consuming ownership and never running its
 /// destructor.
 ///
 /// This function will take ownership of its argument, but is distinct from the
 /// `mem::drop` function in that it **does not run the destructor**, leaking the
 /// value and any resources that it owns.
 ///
 /// There's only a few reasons to use this function. They mainly come
 /// up in unsafe code or FFI code.
 ///
 /// * You have an uninitialized value, perhaps for performance reasons, and
 ///   need to prevent the destructor from running on it.
 /// * You have two copies of a value (like when writing something like
 ///   [`mem::swap`][swap]), but need the destructor to only run once to
 ///   prevent a double `free`.
 /// * Transferring resources across [FFI][ffi] boundaries.
 ///
 /// [swap]: fn.swap.html
 /// [ffi]: ../../book/ffi.html
 ///
 /// # Safety
 ///
 /// This function is not marked as `unsafe` as Rust does not guarantee that the
 /// `Drop` implementation for a value will always run. Note, however, that
 /// leaking resources such as memory or I/O objects is likely not desired, so
 /// this function is only recommended for specialized use cases.
 ///
 /// The safety of this function implies that when writing `unsafe` code
 /// yourself care must be taken when leveraging a destructor that is required to
 /// run to preserve memory safety. There are known situations where the
 /// destructor may not run (such as if ownership of the object with the
 /// destructor is returned) which must be taken into account.
 ///
 /// # Other forms of Leakage
 ///
 /// It's important to point out that this function is not the only method by
 /// which a value can be leaked in safe Rust code. Other known sources of
 /// leakage are:
 ///
 /// * `Rc` and `Arc` cycles
 /// * `mpsc::{Sender, Receiver}` cycles (they use `Arc` internally)
 /// * Panicking destructors are likely to leak local resources
 ///
 /// # Example
 ///
 /// Leak some heap memory by never deallocating it:
 ///
 /// ```rust
 /// use std::mem;
 ///
 /// let heap_memory = Box::new(3);
 /// mem::forget(heap_memory);
 /// ```
 ///
 /// Leak an I/O object, never closing the file:
 ///
 /// ```rust,no_run
 /// use std::mem;
 /// use std::fs::File;
 ///
 /// let file = File::open("foo.txt").unwrap();
 /// mem::forget(file);
 /// ```
 ///
 /// The `mem::swap` function uses `mem::forget` to good effect:
 ///
 /// ```rust
 /// use std::mem;
 /// use std::ptr;
 ///
 /// # #[allow(dead_code)]
 /// fn swap<T>(x: &mut T, y: &mut T) {
 ///     unsafe {
 ///         // Give ourselves some scratch space to work with
 ///         let mut t: T = mem::uninitialized();
 ///
 ///         // Perform the swap, `&mut` pointers never alias
 ///         ptr::copy_nonoverlapping(&*x, &mut t, 1);
 ///         ptr::copy_nonoverlapping(&*y, x, 1);
 ///         ptr::copy_nonoverlapping(&t, y, 1);
 ///
 ///         // y and t now point to the same thing, but we need to completely
 ///         // forget `t` because we do not want to run the destructor for `T`
 ///         // on its value, which is still owned somewhere outside this function.
 ///         mem::forget(t);
 ///     }
 /// }
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn forget<T>(t: T) {
     unsafe { intrinsics::forget(t) }
 }

 /// Returns the size of a type in bytes.
 ///
 /// More specifically, this is the offset in bytes between successive
 /// items of the same type, including alignment padding.
 ///
 /// # Examples
 ///
 /// ```
 /// use std::mem;
 ///
 /// assert_eq!(4, mem::size_of::<i32>());
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn size_of<T>() -> usize {
     unsafe { intrinsics::size_of::<T>() }
 }

 /// Returns the size of the given value in bytes.
 ///
 /// # Examples
 ///
 /// ```
 /// use std::mem;
 ///
 /// assert_eq!(4, mem::size_of_val(&5i32));
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn size_of_val<T: ?Sized>(val: &T) -> usize {
     unsafe { intrinsics::size_of_val(val) }
 }

 /// Returns the ABI-required minimum alignment of a type
 ///
 /// This is the alignment used for struct fields. It may be smaller than the preferred alignment.
 ///
 /// # Examples
 ///
 /// ```
 /// # #![allow(deprecated)]
 /// use std::mem;
 ///
 /// assert_eq!(4, mem::min_align_of::<i32>());
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_deprecated(reason = "use `align_of` instead", since = "1.2.0")]
 pub fn min_align_of<T>() -> usize {
     unsafe { intrinsics::min_align_of::<T>() }
 }

 /// Returns the ABI-required minimum alignment of the type of the value that `val` points to
 ///
 /// # Examples
 ///
 /// ```
 /// # #![allow(deprecated)]
 /// use std::mem;
 ///
 /// assert_eq!(4, mem::min_align_of_val(&5i32));
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_deprecated(reason = "use `align_of_val` instead", since = "1.2.0")]
 pub fn min_align_of_val<T: ?Sized>(val: &T) -> usize {
     unsafe { intrinsics::min_align_of_val(val) }
 }

 /// Returns the alignment in memory for a type.
 ///
 /// This is the alignment used for struct fields. It may be smaller than the preferred alignment.
 ///
 /// # Examples
 ///
 /// ```
 /// use std::mem;
 ///
 /// assert_eq!(4, mem::align_of::<i32>());
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn align_of<T>() -> usize {
     unsafe { intrinsics::min_align_of::<T>() }
 }

 /// Returns the ABI-required minimum alignment of the type of the value that `val` points to
 ///
 /// # Examples
 ///
 /// ```
 /// use std::mem;
 ///
 /// assert_eq!(4, mem::align_of_val(&5i32));
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn align_of_val<T: ?Sized>(val: &T) -> usize {
     unsafe { intrinsics::min_align_of_val(val) }
 }

 /// Creates a value initialized to zero.
 ///
 /// This function is similar to allocating space for a local variable and zeroing it out (an unsafe
 /// operation).
 ///
 /// Care must be taken when using this function, if the type `T` has a destructor and the value
 /// falls out of scope (due to unwinding or returning) before being initialized, then the
 /// destructor will run on zeroed data, likely leading to crashes.
 ///
 /// This is useful for FFI functions sometimes, but should generally be avoided.
 ///
 /// # Examples
 ///
 /// ```
 /// use std::mem;
 ///
 /// let x: i32 = unsafe { mem::zeroed() };
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub unsafe fn zeroed<T>() -> T {
     intrinsics::init()
 }

 /// Creates a value initialized to an unspecified series of bytes.
 ///
 /// The byte sequence usually indicates that the value at the memory
 /// in question has been dropped. Thus, *if* T carries a drop flag,
 /// any associated destructor will not be run when the value falls out
 /// of scope.
 ///
 /// Some code at one time used the `zeroed` function above to
 /// accomplish this goal.
 ///
 /// This function is expected to be deprecated with the transition
 /// to non-zeroing drop.
 #[inline]
 #[unstable(feature = "filling_drop", issue = "5016")]
 pub unsafe fn dropped<T>() -> T {
     #[inline(always)]
     unsafe fn dropped_impl<T>() -> T { intrinsics::init_dropped() }

     dropped_impl()
 }

 /// Bypasses Rust's normal memory-initialization checks by pretending to
 /// produce a value of type T, while doing nothing at all.
 ///
 /// **This is incredibly dangerous, and should not be done lightly. Deeply
 /// consider initializing your memory with a default value instead.**
 ///
 /// This is useful for FFI functions and initializing arrays sometimes,
 /// but should generally be avoided.
 ///
 /// # Undefined Behavior
 ///
 /// It is Undefined Behavior to read uninitialized memory. Even just an
 /// uninitialized boolean. For instance, if you branch on the value of such
 /// a boolean your program may take one, both, or neither of the branches.
 ///
 /// Note that this often also includes *writing* to the uninitialized value.
 /// Rust believes the value is initialized, and will therefore try to Drop
 /// the uninitialized value and its fields if you try to overwrite the memory
 /// in a normal manner. The only way to safely initialize an arbitrary
 /// uninitialized value is with one of the `ptr` functions: `write`, `copy`, or
 /// `copy_nonoverlapping`. This isn't necessary if `T` is a primitive
 /// or otherwise only contains types that don't implement Drop.
 ///
 /// If this value *does* need some kind of Drop, it must be initialized before
 /// it goes out of scope (and therefore would be dropped). Note that this
 /// includes a `panic` occurring and unwinding the stack suddenly.
 ///
 /// # Examples
 ///
 /// Here's how to safely initialize an array of `Vec`s.
 ///
 /// ```
 /// use std::mem;
 /// use std::ptr;
 ///
 /// // Only declare the array. This safely leaves it
 /// // uninitialized in a way that Rust will track for us.
 /// // However we can't initialize it element-by-element
 /// // safely, and we can't use the `[value; 1000]`
 /// // constructor because it only works with `Copy` data.
 /// let mut data: [Vec<u32>; 1000];
 ///
 /// unsafe {
 ///     // So we need to do this to initialize it.
 ///     data = mem::uninitialized();
 ///
 ///     // DANGER ZONE: if anything panics or otherwise
 ///     // incorrectly reads the array here, we will have
 ///     // Undefined Behavior.
 ///
 ///     // It's ok to mutably iterate the data, since this
 ///     // doesn't involve reading it at all.
 ///     // (ptr and len are statically known for arrays)
 ///     for elem in &mut data[..] {
 ///         // *elem = Vec::new() would try to drop the
 ///         // uninitialized memory at `elem` -- bad!
 ///         //
 ///         // Vec::new doesn't allocate or do really
 ///         // anything. It's only safe to call here
 ///         // because we know it won't panic.
 ///         ptr::write(elem, Vec::new());
 ///     }
 ///
 ///     // SAFE ZONE: everything is initialized.
 /// }
 ///
 /// println!("{:?}", &data[0]);
 /// ```
 ///
 /// This example emphasizes exactly how delicate and dangerous doing this is.
 /// Note that the `vec!` macro *does* let you initialize every element with a
 /// value that is only `Clone`, so the following is semantically equivalent and
 /// vastly less dangerous, as long as you can live with an extra heap
 /// allocation:
 ///
 /// ```
 /// let data: Vec<Vec<u32>> = vec![Vec::new(); 1000];
 /// println!("{:?}", &data[0]);
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub unsafe fn uninitialized<T>() -> T {
     intrinsics::uninit()
 }

 /// Swap the values at two mutable locations of the same type, without deinitializing or copying
 /// either one.
 ///
 /// # Examples
 ///
 /// ```
 /// use std::mem;
 ///
 /// let x = &mut 5;
 /// let y = &mut 42;
 ///
 /// mem::swap(x, y);
 ///
 /// assert_eq!(42, *x);
 /// assert_eq!(5, *y);
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn swap<T>(x: &mut T, y: &mut T) {
     unsafe {
         // Give ourselves some scratch space to work with
         let mut t: T = uninitialized();

         // Perform the swap, `&mut` pointers never alias
         ptr::copy_nonoverlapping(&*x, &mut t, 1);
         ptr::copy_nonoverlapping(&*y, x, 1);
         ptr::copy_nonoverlapping(&t, y, 1);

         // y and t now point to the same thing, but we need to completely
         // forget `t` because we do not want to run the destructor for `T`
         // on its value, which is still owned somewhere outside this function.
         forget(t);
     }
 }

 /// Replaces the value at a mutable location with a new one, returning the old value, without
 /// deinitializing or copying either one.
 ///
 /// This is primarily used for transferring and swapping ownership of a value in a mutable
 /// location.
 ///
 /// # Examples
 ///
 /// A simple example:
 ///
 /// ```
 /// use std::mem;
 ///
 /// let mut v: Vec<i32> = Vec::new();
 ///
 /// mem::replace(&mut v, Vec::new());
 /// ```
 ///
 /// This function allows consumption of one field of a struct by replacing it with another value.
 /// The normal approach doesn't always work:
 ///
 /// ```rust,ignore
 /// struct Buffer<T> { buf: Vec<T> }
 ///
 /// impl<T> Buffer<T> {
 ///     fn get_and_reset(&mut self) -> Vec<T> {
 ///         // error: cannot move out of dereference of `&mut`-pointer
 ///         let buf = self.buf;
 ///         self.buf = Vec::new();
 ///         buf
 ///     }
 /// }
 /// ```
 ///
 /// Note that `T` does not necessarily implement `Clone`, so it can't even clone and reset
 /// `self.buf`. But `replace` can be used to disassociate the original value of `self.buf` from
 /// `self`, allowing it to be returned:
 ///
 /// ```
 /// # #![allow(dead_code)]
 /// use std::mem;
 /// # struct Buffer<T> { buf: Vec<T> }
 /// impl<T> Buffer<T> {
 ///     fn get_and_reset(&mut self) -> Vec<T> {
 ///         mem::replace(&mut self.buf, Vec::new())
 ///     }
 /// }
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn replace<T>(dest: &mut T, mut src: T) -> T {
     swap(dest, &mut src);
     src
 }

 /// Disposes of a value.
 ///
 /// While this does call the argument's implementation of `Drop`, it will not
 /// release any borrows, as borrows are based on lexical scope.
 ///
 /// This effectively does nothing for
 /// [types which implement `Copy`](../../book/ownership.html#copy-types),
 /// e.g. integers. Such values are copied and _then_ moved into the function,
 /// so the value persists after this function call.
 ///
 /// # Examples
 ///
 /// Basic usage:
 ///
 /// ```
 /// let v = vec![1, 2, 3];
 ///
 /// drop(v); // explicitly drop the vector
 /// ```
 ///
 /// Borrows are based on lexical scope, so this produces an error:
 ///
 /// ```ignore
 /// let mut v = vec![1, 2, 3];
 /// let x = &v[0];
 ///
 /// drop(x); // explicitly drop the reference, but the borrow still exists
 ///
 /// v.push(4); // error: cannot borrow `v` as mutable because it is also
 ///            // borrowed as immutable
 /// ```
 ///
 /// An inner scope is needed to fix this:
 ///
 /// ```
 /// let mut v = vec![1, 2, 3];
 ///
 /// {
 ///     let x = &v[0];
 ///
 ///     drop(x); // this is now redundant, as `x` is going out of scope anyway
 /// }
 ///
 /// v.push(4); // no problems
 /// ```
 ///
 /// Since `RefCell` enforces the borrow rules at runtime, `drop()` can
 /// seemingly release a borrow of one:
 ///
 /// ```
 /// use std::cell::RefCell;
 ///
 /// let x = RefCell::new(1);
 ///
 /// let mut mutable_borrow = x.borrow_mut();
 /// *mutable_borrow = 1;
 ///
 /// drop(mutable_borrow); // relinquish the mutable borrow on this slot
 ///
 /// let borrow = x.borrow();
 /// println!("{}", *borrow);
 /// ```
 ///
 /// Integers and other types implementing `Copy` are unaffected by `drop()`
 ///
 /// ```
 /// #[derive(Copy, Clone)]
 /// struct Foo(u8);
 ///
 /// let x = 1;
 /// let y = Foo(2);
 /// drop(x); // a copy of `x` is moved and dropped
 /// drop(y); // a copy of `y` is moved and dropped
 ///
 /// println!("x: {}, y: {}", x, y.0); // still available
 /// ```
 ///
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn drop<T>(_x: T) { }

 macro_rules! repeat_u8_as_u16 {
     ($name:expr) => { (($name as u16) <<  8 |
                        ($name as u16)) }
 }
 macro_rules! repeat_u8_as_u32 {
     ($name:expr) => { (($name as u32) << 24 |
                        ($name as u32) << 16 |
                        ($name as u32) <<  8 |
                        ($name as u32)) }
 }
 macro_rules! repeat_u8_as_u64 {
     ($name:expr) => { ((repeat_u8_as_u32!($name) as u64) << 32 |
                        (repeat_u8_as_u32!($name) as u64)) }
 }

 // NOTE: Keep synchronized with values used in librustc_trans::trans::adt.
 //
 // In particular, the POST_DROP_U8 marker must never equal the
 // DTOR_NEEDED_U8 marker.
 //
 // For a while pnkfelix was using 0xc1 here.
 // But having the sign bit set is a pain, so 0x1d is probably better.
 //
 // And of course, 0x00 brings back the old world of zero'ing on drop.
 #[unstable(feature = "filling_drop", issue = "5016")]
 #[allow(missing_docs)]
 pub const POST_DROP_U8: u8 = 0x1d;
 #[unstable(feature = "filling_drop", issue = "5016")]
 #[allow(missing_docs)]
 pub const POST_DROP_U16: u16 = repeat_u8_as_u16!(POST_DROP_U8);
 #[unstable(feature = "filling_drop", issue = "5016")]
 #[allow(missing_docs)]
 pub const POST_DROP_U32: u32 = repeat_u8_as_u32!(POST_DROP_U8);
 #[unstable(feature = "filling_drop", issue = "5016")]
 #[allow(missing_docs)]
 pub const POST_DROP_U64: u64 = repeat_u8_as_u64!(POST_DROP_U8);

 #[cfg(target_pointer_width = "16")]
 #[unstable(feature = "filling_drop", issue = "5016")]
 #[allow(missing_docs)]
 pub const POST_DROP_USIZE: usize = POST_DROP_U16 as usize;
 #[cfg(target_pointer_width = "32")]
 #[unstable(feature = "filling_drop", issue = "5016")]
 #[allow(missing_docs)]
 pub const POST_DROP_USIZE: usize = POST_DROP_U32 as usize;
 #[cfg(target_pointer_width = "64")]
 #[unstable(feature = "filling_drop", issue = "5016")]
 #[allow(missing_docs)]
 pub const POST_DROP_USIZE: usize = POST_DROP_U64 as usize;

 /// Interprets `src` as `&U`, and then reads `src` without moving the contained
 /// value.
 ///
 /// This function will unsafely assume the pointer `src` is valid for
 /// `sizeof(U)` bytes by transmuting `&T` to `&U` and then reading the `&U`. It
 /// will also unsafely create a copy of the contained value instead of moving
 /// out of `src`.
 ///
 /// It is not a compile-time error if `T` and `U` have different sizes, but it
 /// is highly encouraged to only invoke this function where `T` and `U` have the
 /// same size. This function triggers undefined behavior if `U` is larger than
 /// `T`.
 ///
 /// # Examples
 ///
 /// ```
 /// use std::mem;
 ///
 /// #[repr(packed)]
 /// struct Foo {
 ///     bar: u8,
 /// }
 ///
 /// let foo_slice = [10u8];
 ///
 /// unsafe {
 ///     // Copy the data from 'foo_slice' and treat it as a 'Foo'
 ///     let mut foo_struct: Foo = mem::transmute_copy(&foo_slice);
 ///     assert_eq!(foo_struct.bar, 10);
 ///
 ///     // Modify the copied data
 ///     foo_struct.bar = 20;
 ///     assert_eq!(foo_struct.bar, 20);
 /// }
 ///
 /// // The contents of 'foo_slice' should not have changed
 /// assert_eq!(foo_slice, [10]);
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub unsafe fn transmute_copy<T, U>(src: &T) -> U {
     ptr::read(src as *const T as *const U)
 }
	// Copyright 2012-2014 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.

	//! Basic functions for dealing with memory.
	//!
	//! This module contains functions for querying the size and alignment of
	//! types, initializing and manipulating memory.

	#![stable(feature = "rust1", since = "1.0.0")]

	use marker::Sized;
	use intrinsics;
	use ptr;

	#[stable(feature = "rust1", since = "1.0.0")]
	pub use intrinsics::transmute;

	/// Leaks a value into the void, consuming ownership and never running its
	/// destructor.
	///
	/// This function will take ownership of its argument, but is distinct from the
	/// `mem::drop` function in that it does not run the destructor, leaking the
	/// value and any resources that it owns.
	///
	/// There's only a few reasons to use this function. They mainly come
	/// up in unsafe code or FFI code.
	///
	/// * You have an uninitialized value, perhaps for performance reasons, and
	/// need to prevent the destructor from running on it.
	/// * You have two copies of a value (like when writing something like
	/// [`mem::swap`][swap]), but need the destructor to only run once to
	/// prevent a double `free`.
	/// * Transferring resources across [FFI][ffi] boundaries.
	///
	/// [swap]: fn.swap.html
	/// [ffi]: ../../book/ffi.html
	///
	/// # Safety
	///
	/// This function is not marked as `unsafe` as Rust does not guarantee that the
	/// `Drop` implementation for a value will always run. Note, however, that
	/// leaking resources such as memory or I/O objects is likely not desired, so
	/// this function is only recommended for specialized use cases.
	///
	/// The safety of this function implies that when writing `unsafe` code
	/// yourself care must be taken when leveraging a destructor that is required to
	/// run to preserve memory safety. There are known situations where the
	/// destructor may not run (such as if ownership of the object with the
	/// destructor is returned) which must be taken into account.
	///
	/// # Other forms of Leakage
	///
	/// It's important to point out that this function is not the only method by
	/// which a value can be leaked in safe Rust code. Other known sources of
	/// leakage are:
	///
	/// * `Rc` and `Arc` cycles
	/// * `mpsc::{Sender, Receiver}` cycles (they use `Arc` internally)
	/// * Panicking destructors are likely to leak local resources
	///
	/// # Example
	///
	/// Leak some heap memory by never deallocating it:
	///
	/// ```rust
	/// use std::mem;
	///
	/// let heap_memory = Box::new(3);
	/// mem::forget(heap_memory);
	/// ```
	///
	/// Leak an I/O object, never closing the file:
	///
	/// ```rust,no_run
	/// use std::mem;
	/// use std::fs::File;
	///
	/// let file = File::open("foo.txt").unwrap();
	/// mem::forget(file);
	/// ```
	///
	/// The `mem::swap` function uses `mem::forget` to good effect:
	///
	/// ```rust
	/// use std::mem;
	/// use std::ptr;
	///
	/// # #[allow(dead_code)]
	/// fn swap<T>(x: &mut T, y: &mut T) {
	/// unsafe {
	/// // Give ourselves some scratch space to work with
	/// let mut t: T = mem::uninitialized();
	///
	/// // Perform the swap, `&mut` pointers never alias
	/// ptr::copy_nonoverlapping(&*x, &mut t, 1);
	/// ptr::copy_nonoverlapping(&*y, x, 1);
	/// ptr::copy_nonoverlapping(&t, y, 1);
	///
	/// // y and t now point to the same thing, but we need to completely
	/// // forget `t` because we do not want to run the destructor for `T`
	/// // on its value, which is still owned somewhere outside this function.
	/// mem::forget(t);
	/// }
	/// }
	/// ```
	#[inline]
	#[stable(feature = "rust1", since = "1.0.0")]
	pub fn forget<T>(t: T) {
	unsafe { intrinsics::forget(t) }
	}

	/// Returns the size of a type in bytes.
	///
	/// More specifically, this is the offset in bytes between successive
	/// items of the same type, including alignment padding.
	///
	/// # Examples
	///
	/// ```
	/// use std::mem;
	///
	/// assert_eq!(4, mem::size_of::<i32>());
	/// ```
	#[inline]
	#[stable(feature = "rust1", since = "1.0.0")]
	pub fn size_of<T>() -> usize {
	unsafe { intrinsics::size_of::<T>() }
	}

	/// Returns the size of the given value in bytes.
	///
	/// # Examples
	///
	/// ```
	/// use std::mem;
	///
	/// assert_eq!(4, mem::size_of_val(&5i32));
	/// ```
	#[inline]
	#[stable(feature = "rust1", since = "1.0.0")]
	pub fn size_of_val<T: ?Sized>(val: &T) -> usize {
	unsafe { intrinsics::size_of_val(val) }
	}

	/// Returns the ABI-required minimum alignment of a type
	///
	/// This is the alignment used for struct fields. It may be smaller than the preferred alignment.
	///
	/// # Examples
	///
	/// ```
	/// # #![allow(deprecated)]
	/// use std::mem;
	///
	/// assert_eq!(4, mem::min_align_of::<i32>());
	/// ```
	#[inline]
	#[stable(feature = "rust1", since = "1.0.0")]
	#[rustc_deprecated(reason = "use `align_of` instead", since = "1.2.0")]
	pub fn min_align_of<T>() -> usize {
	unsafe { intrinsics::min_align_of::<T>() }
	}

	/// Returns the ABI-required minimum alignment of the type of the value that `val` points to
	///
	/// # Examples
	///
	/// ```
	/// # #![allow(deprecated)]
	/// use std::mem;
	///
	/// assert_eq!(4, mem::min_align_of_val(&5i32));
	/// ```
	#[inline]
	#[stable(feature = "rust1", since = "1.0.0")]
	#[rustc_deprecated(reason = "use `align_of_val` instead", since = "1.2.0")]
	pub fn min_align_of_val<T: ?Sized>(val: &T) -> usize {
	unsafe { intrinsics::min_align_of_val(val) }
	}

	/// Returns the alignment in memory for a type.
	///
	/// This is the alignment used for struct fields. It may be smaller than the preferred alignment.
	///
	/// # Examples
	///
	/// ```
	/// use std::mem;
	///
	/// assert_eq!(4, mem::align_of::<i32>());
	/// ```
	#[inline]
	#[stable(feature = "rust1", since = "1.0.0")]
	pub fn align_of<T>() -> usize {
	unsafe { intrinsics::min_align_of::<T>() }
	}

	/// Returns the ABI-required minimum alignment of the type of the value that `val` points to
	///
	/// # Examples
	///
	/// ```
	/// use std::mem;
	///
	/// assert_eq!(4, mem::align_of_val(&5i32));
	/// ```
	#[inline]
	#[stable(feature = "rust1", since = "1.0.0")]
	pub fn align_of_val<T: ?Sized>(val: &T) -> usize {
	unsafe { intrinsics::min_align_of_val(val) }
	}

	/// Creates a value initialized to zero.
	///
	/// This function is similar to allocating space for a local variable and zeroing it out (an unsafe
	/// operation).
	///
	/// Care must be taken when using this function, if the type `T` has a destructor and the value
	/// falls out of scope (due to unwinding or returning) before being initialized, then the
	/// destructor will run on zeroed data, likely leading to crashes.
	///
	/// This is useful for FFI functions sometimes, but should generally be avoided.
	///
	/// # Examples
	///
	/// ```
	/// use std::mem;
	///
	/// let x: i32 = unsafe { mem::zeroed() };
	/// ```
	#[inline]
	#[stable(feature = "rust1", since = "1.0.0")]
	pub unsafe fn zeroed<T>() -> T {
	intrinsics::init()
	}

	/// Creates a value initialized to an unspecified series of bytes.
	///
	/// The byte sequence usually indicates that the value at the memory
	/// in question has been dropped. Thus, if T carries a drop flag,
	/// any associated destructor will not be run when the value falls out
	/// of scope.
	///
	/// Some code at one time used the `zeroed` function above to
	/// accomplish this goal.
	///
	/// This function is expected to be deprecated with the transition
	/// to non-zeroing drop.
	#[inline]
	#[unstable(feature = "filling_drop", issue = "5016")]
	pub unsafe fn dropped<T>() -> T {
	#[inline(always)]
	unsafe fn dropped_impl<T>() -> T { intrinsics::init_dropped() }

	dropped_impl()
	}

	/// Bypasses Rust's normal memory-initialization checks by pretending to
	/// produce a value of type T, while doing nothing at all.
	///
	/// **This is incredibly dangerous, and should not be done lightly. Deeply
	/// consider initializing your memory with a default value instead.**
	///
	/// This is useful for FFI functions and initializing arrays sometimes,
	/// but should generally be avoided.
	///
	/// # Undefined Behavior
	///
	/// It is Undefined Behavior to read uninitialized memory. Even just an
	/// uninitialized boolean. For instance, if you branch on the value of such
	/// a boolean your program may take one, both, or neither of the branches.
	///
	/// Note that this often also includes writing to the uninitialized value.
	/// Rust believes the value is initialized, and will therefore try to Drop
	/// the uninitialized value and its fields if you try to overwrite the memory
	/// in a normal manner. The only way to safely initialize an arbitrary
	/// uninitialized value is with one of the `ptr` functions: `write`, `copy`, or
	/// `copy_nonoverlapping`. This isn't necessary if `T` is a primitive
	/// or otherwise only contains types that don't implement Drop.
	///
	/// If this value does need some kind of Drop, it must be initialized before
	/// it goes out of scope (and therefore would be dropped). Note that this
	/// includes a `panic` occurring and unwinding the stack suddenly.
	///
	/// # Examples
	///
	/// Here's how to safely initialize an array of `Vec`s.
	///
	/// ```
	/// use std::mem;
	/// use std::ptr;
	///
	/// // Only declare the array. This safely leaves it
	/// // uninitialized in a way that Rust will track for us.
	/// // However we can't initialize it element-by-element
	/// // safely, and we can't use the `[value; 1000]`
	/// // constructor because it only works with `Copy` data.
	/// let mut data: [Vec<u32>; 1000];
	///
	/// unsafe {
	/// // So we need to do this to initialize it.
	/// data = mem::uninitialized();
	///
	/// // DANGER ZONE: if anything panics or otherwise
	/// // incorrectly reads the array here, we will have
	/// // Undefined Behavior.
	///
	/// // It's ok to mutably iterate the data, since this
	/// // doesn't involve reading it at all.
	/// // (ptr and len are statically known for arrays)
	/// for elem in &mut data[..] {
	/// // *elem = Vec::new() would try to drop the
	/// // uninitialized memory at `elem` -- bad!
	/// //
	/// // Vec::new doesn't allocate or do really
	/// // anything. It's only safe to call here
	/// // because we know it won't panic.
	/// ptr::write(elem, Vec::new());
	/// }
	///
	/// // SAFE ZONE: everything is initialized.
	/// }
	///
	/// println!("{:?}", &data[0]);
	/// ```
	///
	/// This example emphasizes exactly how delicate and dangerous doing this is.
	/// Note that the `vec!` macro does let you initialize every element with a
	/// value that is only `Clone`, so the following is semantically equivalent and
	/// vastly less dangerous, as long as you can live with an extra heap
	/// allocation:
	///
	/// ```
	/// let data: Vec<Vec<u32>> = vec![Vec::new(); 1000];
	/// println!("{:?}", &data[0]);
	/// ```
	#[inline]
	#[stable(feature = "rust1", since = "1.0.0")]
	pub unsafe fn uninitialized<T>() -> T {
	intrinsics::uninit()
	}

	/// Swap the values at two mutable locations of the same type, without deinitializing or copying
	/// either one.
	///
	/// # Examples
	///
	/// ```
	/// use std::mem;
	///
	/// let x = &mut 5;
	/// let y = &mut 42;
	///
	/// mem::swap(x, y);
	///
	/// assert_eq!(42, *x);
	/// assert_eq!(5, *y);
	/// ```
	#[inline]
	#[stable(feature = "rust1", since = "1.0.0")]
	pub fn swap<T>(x: &mut T, y: &mut T) {
	unsafe {
	// Give ourselves some scratch space to work with
	let mut t: T = uninitialized();

	// Perform the swap, `&mut` pointers never alias
	ptr::copy_nonoverlapping(&*x, &mut t, 1);
	ptr::copy_nonoverlapping(&*y, x, 1);
	ptr::copy_nonoverlapping(&t, y, 1);

	// y and t now point to the same thing, but we need to completely
	// forget `t` because we do not want to run the destructor for `T`
	// on its value, which is still owned somewhere outside this function.
	forget(t);
	}
	}

	/// Replaces the value at a mutable location with a new one, returning the old value, without
	/// deinitializing or copying either one.
	///
	/// This is primarily used for transferring and swapping ownership of a value in a mutable
	/// location.
	///
	/// # Examples
	///
	/// A simple example:
	///
	/// ```
	/// use std::mem;
	///
	/// let mut v: Vec<i32> = Vec::new();
	///
	/// mem::replace(&mut v, Vec::new());
	/// ```
	///
	/// This function allows consumption of one field of a struct by replacing it with another value.
	/// The normal approach doesn't always work:
	///
	/// ```rust,ignore
	/// struct Buffer<T> { buf: Vec<T> }
	///
	/// impl<T> Buffer<T> {
	/// fn get_and_reset(&mut self) -> Vec<T> {
	/// // error: cannot move out of dereference of `&mut`-pointer
	/// let buf = self.buf;
	/// self.buf = Vec::new();
	/// buf
	/// }
	/// }
	/// ```
	///
	/// Note that `T` does not necessarily implement `Clone`, so it can't even clone and reset
	/// `self.buf`. But `replace` can be used to disassociate the original value of `self.buf` from
	/// `self`, allowing it to be returned:
	///
	/// ```
	/// # #![allow(dead_code)]
	/// use std::mem;
	/// # struct Buffer<T> { buf: Vec<T> }
	/// impl<T> Buffer<T> {
	/// fn get_and_reset(&mut self) -> Vec<T> {
	/// mem::replace(&mut self.buf, Vec::new())
	/// }
	/// }
	/// ```
	#[inline]
	#[stable(feature = "rust1", since = "1.0.0")]
	pub fn replace<T>(dest: &mut T, mut src: T) -> T {
	swap(dest, &mut src);
	src
	}

	/// Disposes of a value.
	///
	/// While this does call the argument's implementation of `Drop`, it will not
	/// release any borrows, as borrows are based on lexical scope.
	///
	/// This effectively does nothing for
	/// [types which implement `Copy`](../../book/ownership.html#copy-types),
	/// e.g. integers. Such values are copied and _then_ moved into the function,
	/// so the value persists after this function call.
	///
	/// # Examples
	///
	/// Basic usage:
	///
	/// ```
	/// let v = vec![1, 2, 3];
	///
	/// drop(v); // explicitly drop the vector
	/// ```
	///
	/// Borrows are based on lexical scope, so this produces an error:
	///
	/// ```ignore
	/// let mut v = vec![1, 2, 3];
	/// let x = &v[0];
	///
	/// drop(x); // explicitly drop the reference, but the borrow still exists
	///
	/// v.push(4); // error: cannot borrow `v` as mutable because it is also
	/// // borrowed as immutable
	/// ```
	///
	/// An inner scope is needed to fix this:
	///
	/// ```
	/// let mut v = vec![1, 2, 3];
	///
	/// {
	/// let x = &v[0];
	///
	/// drop(x); // this is now redundant, as `x` is going out of scope anyway
	/// }
	///
	/// v.push(4); // no problems
	/// ```
	///
	/// Since `RefCell` enforces the borrow rules at runtime, `drop()` can
	/// seemingly release a borrow of one:
	///
	/// ```
	/// use std::cell::RefCell;
	///
	/// let x = RefCell::new(1);
	///
	/// let mut mutable_borrow = x.borrow_mut();
	/// *mutable_borrow = 1;
	///
	/// drop(mutable_borrow); // relinquish the mutable borrow on this slot
	///
	/// let borrow = x.borrow();
	/// println!("{}", *borrow);
	/// ```
	///
	/// Integers and other types implementing `Copy` are unaffected by `drop()`
	///
	/// ```
	/// #[derive(Copy, Clone)]
	/// struct Foo(u8);
	///
	/// let x = 1;
	/// let y = Foo(2);
	/// drop(x); // a copy of `x` is moved and dropped
	/// drop(y); // a copy of `y` is moved and dropped
	///
	/// println!("x: {}, y: {}", x, y.0); // still available
	/// ```
	///
	#[inline]
	#[stable(feature = "rust1", since = "1.0.0")]
	pub fn drop<T>(_x: T) { }

	macro_rules! repeat_u8_as_u16 {
	($name:expr) => { (($name as u16) << 8 \|
	($name as u16)) }
	}
	macro_rules! repeat_u8_as_u32 {
	($name:expr) => { (($name as u32) << 24 \|
	($name as u32) << 16 \|
	($name as u32) << 8 \|
	($name as u32)) }
	}
	macro_rules! repeat_u8_as_u64 {
	($name:expr) => { ((repeat_u8_as_u32!($name) as u64) << 32 \|
	(repeat_u8_as_u32!($name) as u64)) }
	}

	// NOTE: Keep synchronized with values used in librustc_trans::trans::adt.
	//
	// In particular, the POST_DROP_U8 marker must never equal the
	// DTOR_NEEDED_U8 marker.
	//
	// For a while pnkfelix was using 0xc1 here.
	// But having the sign bit set is a pain, so 0x1d is probably better.
	//
	// And of course, 0x00 brings back the old world of zero'ing on drop.
	#[unstable(feature = "filling_drop", issue = "5016")]
	#[allow(missing_docs)]
	pub const POST_DROP_U8: u8 = 0x1d;
	#[unstable(feature = "filling_drop", issue = "5016")]
	#[allow(missing_docs)]
	pub const POST_DROP_U16: u16 = repeat_u8_as_u16!(POST_DROP_U8);
	#[unstable(feature = "filling_drop", issue = "5016")]
	#[allow(missing_docs)]
	pub const POST_DROP_U32: u32 = repeat_u8_as_u32!(POST_DROP_U8);
	#[unstable(feature = "filling_drop", issue = "5016")]
	#[allow(missing_docs)]
	pub const POST_DROP_U64: u64 = repeat_u8_as_u64!(POST_DROP_U8);

	#[cfg(target_pointer_width = "16")]
	#[unstable(feature = "filling_drop", issue = "5016")]
	#[allow(missing_docs)]
	pub const POST_DROP_USIZE: usize = POST_DROP_U16 as usize;
	#[cfg(target_pointer_width = "32")]
	#[unstable(feature = "filling_drop", issue = "5016")]
	#[allow(missing_docs)]
	pub const POST_DROP_USIZE: usize = POST_DROP_U32 as usize;
	#[cfg(target_pointer_width = "64")]
	#[unstable(feature = "filling_drop", issue = "5016")]
	#[allow(missing_docs)]
	pub const POST_DROP_USIZE: usize = POST_DROP_U64 as usize;

	/// Interprets `src` as `&U`, and then reads `src` without moving the contained
	/// value.
	///
	/// This function will unsafely assume the pointer `src` is valid for
	/// `sizeof(U)` bytes by transmuting `&T` to `&U` and then reading the `&U`. It
	/// will also unsafely create a copy of the contained value instead of moving
	/// out of `src`.
	///
	/// It is not a compile-time error if `T` and `U` have different sizes, but it
	/// is highly encouraged to only invoke this function where `T` and `U` have the
	/// same size. This function triggers undefined behavior if `U` is larger than
	/// `T`.
	///
	/// # Examples
	///
	/// ```
	/// use std::mem;
	///
	/// #[repr(packed)]
	/// struct Foo {
	/// bar: u8,
	/// }
	///
	/// let foo_slice = [10u8];
	///
	/// unsafe {
	/// // Copy the data from 'foo_slice' and treat it as a 'Foo'
	/// let mut foo_struct: Foo = mem::transmute_copy(&foo_slice);
	/// assert_eq!(foo_struct.bar, 10);
	///
	/// // Modify the copied data
	/// foo_struct.bar = 20;
	/// assert_eq!(foo_struct.bar, 20);
	/// }
	///
	/// // The contents of 'foo_slice' should not have changed
	/// assert_eq!(foo_slice, [10]);
	/// ```
	#[inline]
	#[stable(feature = "rust1", since = "1.0.0")]
	pub unsafe fn transmute_copy<T, U>(src: &T) -> U {
	ptr::read(src as const T as const U)
	}