ref不能做什么呢?

问题描述

ref 不能做什么引用?可以

What can ref do that references couldn't? Could

match value.try_thing() {
    &Some(ref e) => do_stuff(e),
    // ...
}

不能等同地表达为

match value.try_thing() {
    &Some(e) => do_stuff(&e),
    // ...
}

推荐答案

否，建议的语法无法避免.您的语法不允许引用，否则将允许移动.在此示例中， inner 是 val 中整数的副本，对其进行更改不会影响 val :

No, it is not avoidable with your proposed syntax. Your syntax does not allow for taking a reference when otherwise a move would be permissable. In this example, inner is a copy of the integer from val and changing it has no effect on val:

fn main() {
    let mut val = Some(42);

    if let &mut Some(mut inner) = &mut val {
        inner += 1;
    }

    println!("{:?}", val); // Some(42)
}

需要 ref 关键字来强制引用:

The ref keyword is needed to force taking a reference:

fn main() {
    let mut val = Some(42);

    if let &mut Some(ref mut inner) = &mut val {
        *inner += 1;
    }

    println!("{:?}", val); // Some(43)
}

匹配人体工程学允许以更简单的方式编写代码:

Match ergonomics allows writing this in a simpler manner:

fn main() {
    let mut val = Some(42);

    if let Some(inner) = &mut val {
        *inner += 1;
    }

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

但是，如果我们仅以这种语法开头，那么我们可能会遇到相反的问题和关键字，一个是强制移动.也许 Some(向内移动).在那个替代的宇宙中，会有一个问题问 move 关键字是否可以避免.

However, if we started with only this syntax, then we'd probably have the opposite problem and keyword, one to force a move instead; perhaps Some(move inner). In that alternate universe, there'd be a question asking if the move keyword was avoidable.

另请参阅:

• 在采用& self或& mut self的函数中进行模式匹配时，如何避免使用ref关键字?
• Rust模式匹配如何确定绑定变量是引用还是值?
• 为什么在模式匹配中使用ref而不是星号?
• 引用枚举时要匹配的语法是什么?
• 举例":引用模式

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