Rust中部分移动的值和移动值之间是否有任何区别？

目前在Rust master(0.10-pre)中,当你移动一个唯一向量的一个元素并尝试移动另一个元素时,编译器会抱怨：

let x = ~[~1, ~2, ~3];
let z0 = x[0];
let z1 = x[1]; // error: use of partially moved value: `x`

此错误消息与您移动整个向量有些不同：

let y = ~[~1, ~2, ~3];
let y1 = y;
let y2 = y; // error: use of moved value `y`

为什么不同的消息？如果在第一个例子中x只是“部分移动”,有没有办法“部分移动”x的不同部分？如果没有,为什么不说x被移动？

If x is only “partially moved” in the first example, is there any way
to “partially move” different parts of x?

是的,有,但只有当你同时移动这些部件时：

let x = ~[~1, ~2, ~3];
match x {
    [x1, x2, x3] => println!("{} {} {}", *x1, *x2, *x3),
    _ => unreachable!()
}

可以很容易地发现xN实际上是移出的,因为如果你在匹配后添加额外的行：

println!("{:?}", x);

编译器将抛出一个错误：

main3.rs:16:22: 16:23 error: use of partially moved value: `x`
main3.rs:16     println!("{:?}", x);
                                 ^
note: in expansion of format_args!
<std-macros>:195:27: 195:81 note: expansion site
<std-macros>:194:5: 196:6 note: in expansion of println!
main3.rs:16:5: 16:25 note: expansion site
main3.rs:13:10: 13:12 note: `(*x)[]` moved here because it has type `~int`, which is moved by default (use `ref` to override)
main3.rs:13         [x1, x2, x3] => println!("{} {} {}", *x1, *x2, *x3),
                     ^~
error: aborting due to previous error

结构和枚举也是如此 – 它们也可以部分移动.