是否可以收集迭代器以向后填充集合? [英] Is it possible to collect an iterator to populate a collection backwards?

问题描述

是否有可能收集一个迭代器，以使其向后填充集合，例如在VecDeque中使用push_front?

Is it possible to collect an iterator such that it populates a collection backwards, such as using push_front in a VecDeque?

有可能收集到Vec中然后将其反转，但是对于显式支持此功能的数据结构来说，似乎没有必要.如果可能的话，我想避免编写一个显式的for循环.

It's possible to collect into a Vec and then reverse it, but it seems like it should be unnecessary with data structures explicitly supporting this capability. I'd like to avoid writing an explicit for loop if possible.

推荐答案

是的，有可能:

use std::collections::VecDeque;

fn main() {
    let v: VecDeque<_> = (0..=2).collect_rev();
    assert_eq!(v, [2, 1, 0]);

    let v: Vec<_> = (0..=2).collect_rev();
    assert_eq!(v, [2, 1, 0]);
}

您只需要一点胶水代码:

You just need a bit of glue code:

trait CollectRev: Iterator {
    fn collect_rev<B>(self) -> B
    where
        B: FromIteratorRev<Self::Item>,
        Self: Sized,
    {
        B::from_iter_rev(self)
    }
}

impl<I: Iterator> CollectRev for I {}

trait FromIteratorRev<T> {
    fn from_iter_rev(iter: impl IntoIterator<Item = T>) -> Self;
}

并有效地将其实现为各种类型:

And implement it efficiently for various types:

impl<T> FromIteratorRev<T> for VecDeque<T> {
    fn from_iter_rev(iter: impl IntoIterator<Item = T>) -> Self {
        let mut v = Self::new();
        for i in iter {
            v.push_front(i);
        }
        v
    }
}

impl<T> FromIteratorRev<T> for Vec<T> {
    fn from_iter_rev(iter: impl IntoIterator<Item = T>) -> Self {
        let mut v: Self = iter.into_iter().collect();
        v.reverse();
        v
    }
}

我想避免编写明确的for循环

必须要编写该代码.

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