How to create and fire event listener

help
7

The final code worked with me is as per this playground:

//#[derive(Debug)]
pub struct Counter {
 count: i32,
}

impl std::fmt::Debug for Counter {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "Counter `count` is: {}", self.count)
    }
}

trait EventEmitter {
    fn square(&mut self);
    fn increase(&mut self, amount: i32);
    fn decrease(&mut self, amount: i32);
    fn change_by(&mut self, amount: i32);
}

impl EventEmitter for Counter {
    fn square(&mut self) { 
        self.count = self.count.pow(2);
        Self::on_squared();
    }
    fn increase(&mut self, amount: i32) { 
        self.count += amount; 
        Self::on_increased(amount);
    }
    fn decrease(&mut self, amount: i32) {
        let initial_value = self.count;
        self.count -= amount;
        Self::on_decreased(Self {count: initial_value}, amount);
    }
    fn change_by(&mut self, amount: i32) {
        let initial_value = self.count;
        self.count += amount;
        match amount {
            x if x > 0 => Self::on_increased(amount),
            x if x < 0 => Self::on_decreased(Self {count: initial_value}, amount.abs()),
            _          => println!("No changes")
        }
    }
}

trait EventListener {
     fn on_squared() {
        println!("Counter squared")
     }
     fn on_increased(amount: i32) {
        println!("Counter increased by {}", amount)
     }
     fn on_decreased(self, amount: i32);
}

impl EventListener for Counter {
    fn on_decreased(self, amount: i32) {
        println!("Counter reduced from {} to {}", &self.count, &self.count - amount)
    }
}

fn main() {
    let mut x = Counter { count: 5 };
    println!("Counter started at: {:#?}", x.count);
    x.square();
    println!("{:?}", x);
    x.increase(3);
    println!("{:?}", x);
    x.decrease(2);
    println!("{:?}", x);
    x.change_by(-1);
    println!("{:?}", x);
}

And got the below output:

Counter started at: 5
Counter squared
Counter `count` is: 25
Counter increased by 3
Counter `count` is: 28
Counter reduced from 28 to 26
Counter `count` is: 26
Counter reduced from 26 to 25
Counter `count` is: 25