是否可以围绕 &mut 创建一个包装器，它的作用类似于 &mut [英] Is it possible to create a wrapper around an &mut that acts like an &mut

问题描述

以下代码无法编译，因为 MutRef 不是 Copy.无法复制，因为 &'a mut i32 不是 Copy.有没有办法给 MutRef 类似的语义给 &'a mut i32 ?

The following code fails to compile because MutRef is not Copy. It can not be made copy because &'a mut i32 is not Copy. Is there any way give MutRef similar semantics to &'a mut i32?

这样做的动机是能够将大量函数参数打包成一个结构体，以便它们可以作为一个组传递，而无需单独传递.

The motivation for this is being able to package up a large set of function parameters into a struct so that they can be passed as a group instead of needing to be passed individually.

struct MutRef<'a> {
    v: &'a mut i32
}

fn wrapper_use(s: MutRef) {
}

fn raw_use(s: &mut i32) {
}

fn raw_ref() {
    let mut s: i32 = 9;
    let q = &mut s;
    raw_use(q);
    raw_use(q);

}

fn wrapper() {
    let mut s: i32 = 9;
    let q = MutRef{ v: &mut s };
    wrapper_use(q);
    wrapper_use(q);
}

推荐答案

没有

此功能的名称是隐式再借用"，当您传递一个 &mut 引用时，编译器需要一个可能的 &mut 引用时会发生这种情况.不一样的人生.只有当实际类型和预期类型都是 &mut 引用时，编译器才会隐式地重新借用.它不适用于 generic参数 或包含 &mut 引用的结构.当前的 Rust 没有办法创建可以隐式重新借用的自定义类型.

The name for this feature is "implicit reborrowing" and it happens when you pass a &mut reference where the compiler expects a &mut reference of a possibly different lifetime. The compiler only implicitly reborrows when the actual type and the expected type are both &mut references. It does not work with generic arguments or structs that contain &mut references. There is no way in current Rust to make a custom type that can be implicitly reborrowed.

但是，您可以实现自己的方法来显式重新借用:

However, you can implement your own method to explicitly reborrow:

impl<'a> MutRef<'a> {
    // equivalent to fn reborrow(&mut self) -> MutRef<'_>
    fn reborrow<'b>(&'b mut self) -> MutRef<'b> {
        MutRef {v: self.v}
    }
}

fn wrapper() {
    let mut s: i32 = 9;
    let mut q = MutRef{ v: &mut s };
    wrapper_use(q.reborrow());  // does not move q
    wrapper_use(q);             // moves q
}

另见

• 为什么这里没有移动可变引用?
• 类型推断和借用与所有权转让

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