rust - Rust 中 ".map(|&x| x)"的目的是什么

Question

我正在学习 Rust，并在许多地方注意到以下迭代器模式:

let some_vector: &[& str] = &["hello", "world", "zombies", "pants"];
let result: Vec<&str> = some_vector
    .iter()
    .filter(|&x| *x == "hello")
    .map(|&x| x)
    .collect();

那个.map(|&x| x)的目的是什么？为什么有必要？它会创建副本吗？

当我删除它时，我得到以下编译器错误:

error[E0277]: a value of type `Vec<&str>` cannot be built from an iterator over elements of type `&&str`
    --> src/main.rs:7:6
     |
7    |     .collect();
     |      ^^^^^^^ value of type `Vec<&str>` cannot be built from `std::iter::Iterator<Item=&&str>`
     |
     = help: the trait `FromIterator<&&str>` is not implemented for `Vec<&str>`
note: required by a bound in `collect`

For more information about this error, try `rustc --explain E0277`.

所以 map 将一个迭代器对字符串切片的引用转换为一个迭代器对字符串切片？删除一级间接？对吗？

Answer 1

除了@AlexW 的回答，实际上没有必要写，因为有一个内置的迭代器适配器可以做得更好(更清晰，更高效):copied() .

let some_vector: &[&str] = &["hello", "world", "zombies", "pants"];
let result: Vec<&str> = some_vector
    .iter()
    .filter(|&x| *x == "hello")
    .copied()
    .collect();

还有cloned()等于 .map(|x| x.clone()).