Rust进阶(5)-迭代器

迭代器

概述

1. 迭代器负责遍历序列中的每一项和决定序列何时结束的逻辑
2. 创建迭代器：迭代器是惰性的，意思就是在调用方法使用迭代器之前，不会有任何效果
3. 每个迭代器都实现了iterator trait，iterator trait定义在标准库中：

//next是Iterator被要求实现的唯一一个方法，next一次返回一个元素，当迭代器结束时，返回None
trait Iterator{
    type Item;
    fn next(mut self) -> Option<Self::Item>; //type Item和Self::Item这种用法叫做定义trait的关联类型
}

基本使用

fn main() {
    let v1 = vec![1, 2, 3];
    let mut v1_iter = v1.iter(); //到目前为止，不会对v1产生任何影响
    /*for val in v1_iter{
        println!("val = {}", val)
    }*/

    if let Some(v) = v1_iter.next() {
        println!("v = {}", v);//1
    }
    if let Some(v) = v1_iter.next() {
        println!("v = {}", v);//2
    }
    if let Some(v) = v1_iter.next() {
        println!("v = {}", v);//3
    }
    if let Some(v) = v1_iter.next() {
        println!("v = {}", v);
    } else {
        println!("At End");
    }

    let mut v2 = vec![1, 2, 3];
    let mut v2_iter = v2.iter_mut();
    if let Some(v) = v2_iter.next() {
        *v = 3;
    }
    println!("v2 = {:?}", v2);

    //消费适配器
    let v1 = vec![1, 2, 3];
    let v1_iter = v1.iter();
    let total: i32 = v1_iter.sum(); //调用消费适配器sum来求和
    println!("total = {}", total);

    //迭代适配器
    let v1 = vec![1, 2, 3];
    println!("v1 = {:?}", v1);
    let v2: Vec<_> = v1.iter().map(|x| x + 1).collect();
    println!("v2 = {:?}", v2);

    //过滤
    let v1 = vec![1,12, 45];
    println!("v1 = {:?}", v1);
    let v2: Vec<_> = v1.into_iter().filter(|x| *x>5).collect();
    println!("v2 = {:?}", v2);
}

自定义迭代器

struct Counter {
    count: u32,
}

impl Counter {
    fn new() -> Counter {
        Counter { count: 0 }
    }
}

impl Iterator for Counter {
    type Item = u32;
    fn next(&mut self) -> Option<Self::Item> {
        self.count += 1;
        if self.count < 6 {
            Some(self.count)
        } else {
            None
        }
    }
}

fn main() {
    let mut counter = Counter::new();
    for i in 0..6 {
        if let Some(v) = counter.next() {
            println!("i = {}, v = {}", i, v);
        } else {
            println!("i = {}, at end", i);
            break;
        }
    }
}

总结

本文编辑完毕

参考

[1] Rust 程序设计语言