一个 for 循环如何借用迭代器? [英] How does one have a for loop borrow the iterator?

问题描述

如何让 for ... in 循环借用它正在操作的迭代器?例如:

How does one have a for ... in loop borrow the iterator it is operating over? For example:

let x = vec![1, 2, 3, 4];
let i = x.iter();
for a1 in i { break; } // iterate over just one "i"
for a2 in i { break; } // continue iterating through "i" here

您不能简单地将 &i 赋予 for，因为这样就无法将 &Iterator 转换为 Iterator> 对象.

You can't simply give &i to the for, because then it can't convert the &Iterator to an Iterator object.

推荐答案

您可以使用 Iterator::by_ref 借用迭代器，借用结束后继续使用:

You can use Iterator::by_ref to borrow the iterator and continue to use it after the borrow ends:

fn main() {
    let x = vec![1, 2, 3, 4];
    let mut i = x.iter();
    for _ in i.by_ref() { break; } // iterate over just one "i"
    for _ in i.by_ref() { break; } // continue iterating through "i" here
    assert_eq!(Some(&3), i.next())
}

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