diff --git a/src/libcore/mem/mod.rs b/src/libcore/mem/mod.rs index b43ba6ac34032..770d1ca8e7501 100644 --- a/src/libcore/mem/mod.rs +++ b/src/libcore/mem/mod.rs @@ -503,6 +503,61 @@ pub fn swap(x: &mut T, y: &mut T) { } } +/// Replace `dest` with the default value of `T`, and return the previous `dest` value. +/// +/// # Examples +/// +/// A simple example: +/// +/// ``` +/// use std::mem; +/// +/// let mut v: Vec = vec![1, 2]; +/// +/// let old_v = mem::take(&mut v); +/// assert_eq!(vec![1, 2], old_v); +/// assert!(v.is_empty()); +/// ``` +/// +/// `take` allows taking ownership of a struct field by replacing it with an "empty" value. +/// Without `take` you can run into issues like these: +/// +/// ```compile_fail,E0507 +/// struct Buffer { buf: Vec } +/// +/// impl Buffer { +/// fn get_and_reset(&mut self) -> Vec { +/// // 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 `take` 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 { buf: Vec } +/// impl Buffer { +/// fn get_and_reset(&mut self) -> Vec { +/// mem::take(&mut self.buf) +/// } +/// } +/// ``` +/// +/// [`Clone`]: ../../std/clone/trait.Clone.html +#[inline] +#[unstable(feature = "mem_take", issue = "61129")] +pub fn take(dest: &mut T) -> T { + replace(dest, T::default()) +} + /// Moves `src` into the referenced `dest`, returning the previous `dest` value. /// /// Neither value is dropped.