这个功能有点高级，
暂时理解不完全，
先把代码练正确吧。
use std::thread; use std::time::Duration; struct Cacher<T> where T: Fn(u32) -> u32 { caculation: T, value: Option<u32>, } impl<T> Cacher<T> where T: Fn(u32) -> u32 { fn new(caculation: T) -> Cacher<T> { Cacher { caculation, value: None, } } fn value(&mut self, arg: u32) -> u32 { match self.value { Some(v) => v, None => { let v = (self.caculation)(arg); self.value = Some(v); v }, } } } fn main() { let simulated_user_specified_value = 6; let simulated_random_number = 30; generate_workout( simulated_user_specified_value, simulated_random_number ); } fn generate_workout(intensity: u32, random_number: u32) { let mut expensive_result = Cacher::new(|num| { println!("calculating slowly..."); thread::sleep(Duration::from_secs(2)); num }); if intensity < 25 { println!("Today, do {} pushups", expensive_result.value(intensity)); println!("Next, do {} situps!", expensive_result.value(intensity)); } else { if random_number == 3 { println!("Take a break today! Remember to stay hydrated!"); } else { println!("Today, run for {} minutes!", expensive_result.value(intensity)); } } } /* fn simulated_expensive_calculation(num: u32) -> u32 { println!("calculating slowly..."); thread::sleep(Duration::from_secs(2)); num } */
来源：博客园
作者：aguncn
链接：https://www.cnblogs.com/aguncn/p/11438380.html