closures_with_fn_trait_obj.rs

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


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, args: u32) -> u32 {
        match self.value {
            Some(v) => v,
            None => {
                let val = (self.calculation)(args);
                self.value = Some(val);
                val
            }
        }
    }
}

fn generate_workout(intensity: u32, random_number: u32) {
    let mut expensive_result = Cacher::new(|num| {
        println!("[!!] Calculating very slow..");
        thread::sleep(Duration::from_secs(2));
        num
    });
    if intensity < 25 {
        println!("Do {} pushups",expensive_result.value(intensity));
        println!("Do {} situps",expensive_result.value(intensity));
    }else {
        if random_number == 3 {
            println!("[+] Take rest today, remember to stay hydrated!!");
        }else {
            println!("[+] Do the running for {} minutes",expensive_result.value(intensity));
        }
    }
}



fn main() {
    let simulated_high_number = 22;
    let simulated_random_number = 4;
    generate_workout(simulated_high_number, simulated_random_number)
}