如何根据 Peekable::peek 的结果调用 Peekable::next?

问题描述

use std::iter::Peekable;

pub trait AdvanceWhile<I: Iterator> {
    fn advance_while<P>(&mut self, predicate: P)
    where
        P: Fn(&I::Item) -> bool;
}

impl<I: Iterator> AdvanceWhile<I> for Peekable<I> {
    fn advance_while<P>(&mut self, predicate: P)
    where
        P: Fn(&I::Item) -> bool,
    {
        while let Some(val) = self.peek() {
            if predicate(val) {
                self.next();
            } else {
                break;
            }
        }
    }
}

游乐场

错误:

error[E0499]: cannot borrow `*self` as mutable more than once at a time
  --> src/main.rs:16:17
   |
14 |         while let Some(val) = self.peek() {
   |                               ---- first mutable borrow occurs here
15 |             if predicate(val) {
16 |                 self.next();
   |                 ^^^^ second mutable borrow occurs here
...
20 |         }
   |         - first borrow ends here

推荐答案

正如 Lukas Kalbertodt 已经说过的，这是一个借用检查器的限制.这里我想展示一个更易读的版本:

As Lukas Kalbertodt already said, this is a limitation of the borrow checker. Here I would like to show a more readable version:

fn advance_while<P>(&mut self, predicate: P)
    where P: Fn(&I::Item) -> bool
{
    while let Some(true) = self.peek().map(&predicate) {
        self.next();
    }
}

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