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// 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] use kinds::Sized; use intrinsics; use ptr; #[stable] pub use intrinsics::transmute; /// Moves a thing into the void. /// /// The forget function will take ownership of the provided value but neglect /// to run any required cleanup or memory management operations on it. /// /// This function is the unsafe version of the `drop` function because it does /// not run any destructors. #[stable] pub use intrinsics::forget; /// Returns the size of a type in bytes. /// /// # Examples /// /// ``` /// use std::mem; /// /// assert_eq!(4, mem::size_of::<i32>()); /// ``` #[inline] #[stable] pub fn size_of<T>() -> uint { unsafe { intrinsics::size_of::<T>() } } /// Returns the size of the type that `_val` points to in bytes. /// /// # Examples /// /// ``` /// use std::mem; /// /// assert_eq!(4, mem::size_of_val(&5i32)); /// ``` #[inline] #[stable] pub fn size_of_val<T>(_val: &T) -> uint { size_of::<T>() } /// 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 /// /// ``` /// use std::mem; /// /// assert_eq!(4, mem::min_align_of::<i32>()); /// ``` #[inline] #[stable] pub fn min_align_of<T>() -> uint { 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::min_align_of_val(&5i32)); /// ``` #[inline] #[stable] pub fn min_align_of_val<T>(_val: &T) -> uint { min_align_of::<T>() } /// Returns the alignment in memory for a type. /// /// This function will return the alignment, in bytes, of a type in memory. If the alignment /// returned is adhered to, then the type is guaranteed to function properly. /// /// # Examples /// /// ``` /// use std::mem; /// /// assert_eq!(4, mem::align_of::<i32>()); /// ``` #[inline] #[stable] pub fn align_of<T>() -> uint { // We use the preferred alignment as the default alignment for a type. This // appears to be what clang migrated towards as well: // // http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20110725/044411.html unsafe { intrinsics::pref_align_of::<T>() } } /// Returns the alignment of the type of the value that `_val` points to. /// /// This is similar to `align_of`, but function will properly handle types such as trait objects /// (in the future), returning the alignment for an arbitrary value at runtime. /// /// # Examples /// /// ``` /// use std::mem; /// /// assert_eq!(4, mem::align_of_val(&5i32)); /// ``` #[inline] #[stable] pub fn align_of_val<T>(_val: &T) -> uint { align_of::<T>() } /// Create 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: int = unsafe { mem::zeroed() }; /// ``` #[inline] #[stable] pub unsafe fn zeroed<T>() -> T { intrinsics::init() } /// Create an uninitialized value. /// /// 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 uninitialized data, likely leading to crashes. /// /// This is useful for FFI functions sometimes, but should generally be avoided. /// /// # Examples /// /// ``` /// use std::mem; /// /// let x: int = unsafe { mem::uninitialized() }; /// ``` #[inline] #[stable] pub unsafe fn uninitialized<T>() -> T { intrinsics::uninit() } /// Swap the values at two mutable locations of the same type, without deinitialising or copying /// either one. /// /// # Examples /// /// ``` /// use std::mem; /// /// let x = &mut 5i; /// let y = &mut 42i; /// /// mem::swap(x, y); /// /// assert_eq!(42i, *x); /// assert_eq!(5i, *y); /// ``` #[inline] #[stable] 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_memory(&mut t, &*x, 1); ptr::copy_nonoverlapping_memory(x, &*y, 1); ptr::copy_nonoverlapping_memory(y, &t, 1); // y and t now point to the same thing, but we need to completely forget `t` // because it's no longer relevant. forget(t); } } /// Replace the value at a mutable location with a new one, returning the old value, without /// deinitialising 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: /// /// ```rust /// 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] pub fn replace<T>(dest: &mut T, mut src: T) -> T { swap(dest, &mut src); src } /// Disposes of a value. /// /// This function can be used to destroy any value by allowing `drop` to take ownership of its /// argument. /// /// # Examples /// /// ``` /// use std::cell::RefCell; /// /// let x = RefCell::new(1i); /// /// 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); /// ``` #[inline] #[stable] pub fn drop<T>(_x: T) { } /// 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; /// /// let one = unsafe { mem::transmute_copy(&1i) }; /// /// assert_eq!(1u, one); /// ``` #[inline] #[stable] pub unsafe fn transmute_copy<T, U>(src: &T) -> U { ptr::read(src as *const T as *const U) } /// Transforms lifetime of the second pointer to match the first. #[inline] #[unstable = "this function may be removed in the future due to its \ questionable utility"] pub unsafe fn copy_lifetime<'a, Sized? S, Sized? T: 'a>(_ptr: &'a S, ptr: &T) -> &'a T { transmute(ptr) } /// Transforms lifetime of the second mutable pointer to match the first. #[inline] #[unstable = "this function may be removed in the future due to its \ questionable utility"] pub unsafe fn copy_mut_lifetime<'a, Sized? S, Sized? T: 'a>(_ptr: &'a mut S, ptr: &mut T) -> &'a mut T { transmute(ptr) }