Rust 避免内存分配
交换两个变量值
use std::mem;
let mut x = 5;
let mut y = 42;
mem::swap(&mut x, &mut y);
获取变量所有权，原值置空
use std::mem;
let mut v: Vec<i32> = vec![1, 2];
let old_v = mem::take(&mut v);
assert_eq!(vec![1, 2], old_v);
assert!(v.is_empty());
mem::take等价于mem::replace(name, String::new())
获取变量所有权，原值替换
use std::mem;
let mut v: Vec<i32> = vec![1, 2];
let old_v = mem::replace(&mut v, vec![3, 4, 5]);
assert_eq!(vec![1, 2], old_v);
assert_eq!(vec![3, 4, 5], v);
其他
优点：没有内存分配
实际例子：
use std::mem;
enum MultiVariateEnum {
A { name: String },
B { name: String },
C,
D
}
fn swizzle(e: &mut MultiVariateEnum) {
use MultiVariateEnum::*;
*e = match e {
// Ownership rules do not allow taking `name` by value, but we cannot
// take the value out of a mutable reference, unless we replace it:
A { name } => B { name: mem::take(name) },
B { name } => A { name: mem::take(name) },
C => D,
D => C
}
}
