使用自定义步骤迭代范围的稳定方法是什么？ [英] What is a stable way to iterate on a range with custom step?

问题描述

如果我想在稳定的Rust中使用自定义步骤进行迭代，我该怎么办？基本上类似于C / C ++

How should I go if I want to iterate with a custom step in stable Rust? Essentially something like the C/C++

for (int i = 0; i < n; i += 2) {

}

我已经尝试过使用 range_step_inclusive 以及如何使用自定义步骤迭代范围？ ：

I've already tried using range_step_inclusive and the solutions in How do I iterate over a range with a custom step?:

use std::iter::range_step_inclusive;
for i in range_step_inclusive(0, n, 2) {
    println!("i: {}", i);
}

但似乎它在Rust 1.1中不可用：

But it seems like it isn't available in Rust 1.1:

error: unresolved import `std::iter::range_step_inclusive`. There is no `range_step_inclusive` in `std::iter`

什么是替代品？可能是创建自定义范围的惯用方法。

What would be an alternative? Possibly the idiomatic way for creating custom ranges.

推荐答案

Rust 1.28 +

Iterator :: step_by 现在稳定：

Rust 1.28+

Iterator::step_by is now stable:

fn main() {
    for i in (0..100).step_by(2) {
        println!("{}", i);
    }
}

Rust 1.1 +

你总是可以用老式的方式写出来：

Rust 1.1+

You can always write it out the old-fashioned way:

fn main() {
    let mut i = 0;
    while i < 100 {
        println!("i: {}", i);
        i += 2;
    }
}

然后可以抽象出来：

use std::ops::Add;

fn step_by<T, F>(start: T, end_exclusive: T, step: T, mut body: F)
where
    T: Add<Output = T> + PartialOrd + Copy,
    F: FnMut(T),
{
    let mut i = start;
    while i < end_exclusive {
        body(i);
        i = i + step;
    }
}

fn main() {
    step_by(0, 100, 2, |i| {
        println!("i: {}", i);
    })
}

有趣的历史旁注我相信最初所有的循环都是用这样的闭包来完成的，之后迭代器变得非常普遍。

Interesting historical side note, I believe that originally all the looping was done with closures like this, before iterators became extremely prevalent.

然后你可以把它变成迭代器：

You can then take this and make it into an iterator:

use std::ops::Add;

struct StepBy<T> {
    start: T,
    end_exclusive: T,
    step: T,
}

impl<T> StepBy<T> {
    fn new(start: T, end_exclusive: T, step: T) -> Self {
        Self {
            start,
            end_exclusive,
            step,
        }
    }
}

impl<T> Iterator for StepBy<T>
where
    T: Add<Output = T> + PartialOrd + Copy,
{
    type Item = T;
    fn next(&mut self) -> Option<Self::Item> {
        if self.start < self.end_exclusive {
            let v = self.start;
            self.start = self.start + self.step;
            Some(v)
        } else {
            None
        }
    }
}

fn main() {
    for i in StepBy::new(0, 100, 2) {
        println!("i: {}", i);
    }
}

参见：

• 如何向Iterator添加新方法？

• How can I add new methods to Iterator?

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