在Rust中，如何在`iter_mut`上使用‘`find()’

Question

我如何使这个编译：

struct S {
    s:String
}

fn main() {
    let mut v:Vec<S>;
    let cmp = "asdf";
    v.iter_mut().find(|&&x| x == cmp);
    //                 ^^^
    //                 What to write here when using find on a iter_mut (and why?)
}

错误消息：

 --> src/main.rs:8:25
  |
8 |     v.iter_mut().find(|&&x| x == cmp);
  |                         ^-
  |                         ||
  |                         |expected due to this
  |                         types differ in mutability
  |                         help: you can probably remove the explicit borrow: `x`
  |
  = note: expected mutable reference `&mut S`
                     found reference `&_`

For more information about this error, try `rustc --explain E0308`.
error: could not compile `asdf` due to previous error

Answer 1

您不必在闭包中使用变形结构 S，因为这会移动字符串。

struct S {
    s: String,
}

fn main() {
    let mut v: Vec<_> = vec![S { s: "Hello".into() }, S { s: "asdf".into() }];
    let cmp = "asdf";

    // Will be Option<&mut S>
    let _found = v.iter_mut().find(|x| x.s == cmp);
}

我在Vec中添加了两个项，因为您声明了v而没有定义它。注意，闭包只使用x，它是一个&&mut，但是您不必在任何地方显式地这样说，因为x将在闭包的正文中被取消引用。

表达式x.s == cmp比较String，s，从&str到&str，cmp。

// Automatically dereferenced
x.s == cmp

手工操作：

// Manually dereferenced. You don't have to do this for structs.
(**x).s

进一步阅读

• 解构
• 去铁
• PartialEq