Rust语言 学习12 闭包和迭代器

一、闭包入门

use std::thread;
use std::time::Duration;

fn main(){
    let specified_value = 10;
    let random_number = 7;
    generate_workout(specified_value,random_number);

}

fn generate_workout(intensity:u32,random_number:u32) {
    // 定义一个函数闭包
    let expensive_closure = |num| {
        println!("calculate slowly");
        thread::sleep(Duration::from_secs(2));
        num;
    };

    // 然后传入函数闭包
    if intensity < 25 {
        println!("Today,do {} pushups!",expensive_calculate(intensity));
        println!("Next do {} situps!", expensive_calculate(intensity));
    } else {
        if random_number == 3 {
            println!("Take break today");
        } else {
            println!("Today,fun for {} minutes",expensive_calculate(intensity));
        }
    }
}

二、闭包的类型推断和标注

已经推断成String类型，就不能再推断成u32类型了

三、使用泛型参数和Fn Trait来存储闭包

use std::thread;
use std::time::Duration;

// 结构体存储闭包
struct Cacher<T>
where T: Fn(u32) -> u32,
{
    calculation : T,
    value : Option<u32>,
}

impl <T> Cacher<T>
    where T: Fn(u32) -> u32,
{
    fn new(calculation : T) -> Cacher<T> {
        Cacher {
            calculation,
            value : None,
        }
    }

    fn value(&mut self,arg:u32) -> u32 {
        match self.value {
            Some(v) => v,
            None => {
                let v = (self.calculation)(arg);
                self.value = Some(v);
                v
            }
        }
    }
    
}


fn main(){
    let specified_value = 10;
    let random_number = 7;
    generate_workout(specified_value,random_number);

}

fn generate_workout(intensity:u32,random_number:u32) {
    // 定义一个函数闭包
    let mut expensive_closure = Cacher::new(|num| {
        println!("calculate slowly");
        thread::sleep(Duration::from_secs(2));
        num
    });

    // 然后传入函数闭包
    if intensity < 25 {
        println!("Today,do {} pushups!",expensive_closure.value(intensity));
        println!("Next do {} situps!", expensive_closure.value(intensity));
    } else {
        if random_number == 3 {
            println!("Take break today");
        } else {
            println!("Today,fun for {} minutes",expensive_closure.value(intensity));
        }
    }
}

四、使用闭包捕获上下文