counters.rs

trait Counter: 'static {
    fn create(data: &str) -> Self where Self: Sized;
}

struct CounterA(i32);
impl Counter for CounterA {
    fn create(data: &str) -> Self where Self: Sized {
        CounterA(data.parse::<i32>().unwrap())
    }
}

struct CounterB(f64);
impl Counter for CounterB {
    fn create(data: &str) -> Self where Self: Sized {
        CounterB(data.parse::<f64>().unwrap())
    }
}

fn create_counter(name: &str, data: &str) -> Box<Counter> {
    fn create<C: Counter>(data: &str) -> Box<Counter> { Box::new(C::create(data)) }
    let registry: &[(&str, fn(&str) -> Box<Counter>)] = &[
        ("A", create::<CounterA>),
        ("B", create::<CounterB>),
    ];

    for &(n, ctor) in registry {
        if n == name {
            return ctor(data);
        }
    }
    panic!("Unknown counter {}", name)
}


fn main() {
    println!("Hello, world!");
}