// https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=7ccac7cdf77cbc63a7d6fabd75a8b86e

struct Message;

trait Filter {
    type Checking;
    fn check(&self, to_check: &Self::Checking) -> bool;
}

struct SomeFilter<T> {
    handler: fn(&T) -> bool,
}

impl<T> Filter for SomeFilter<T> {
    type Checking = T;
    fn check(&self, to_check: &Self::Checking) -> bool {
        (self.handler)(to_check)
    }
}

struct Handler<T> {
    filters: Vec<Box<dyn Filter<Checking = T>>>,
    handler: fn(&T) -> bool,
}

impl<T> Handler<T> {
    fn run(&self, message: &T) -> Option<bool> {
        for filter in &self.filters {
            let _result = filter.check(message);
            if !_result {
                return None;
            }
        }

        Some((self.handler)(message))
    }
}

fn main() {
    let filter_always_true = Box::new(SomeFilter {
        handler: |_msg: &Message| true,
    }) as Box<dyn Filter<Checking=Message>>;
    
    let filters = vec![filter_always_true];
    let msg_handler = Handler::<Message> {
        filters: filters,
        handler: |_msg: &Message| true,
    };

    println!("{}", msg_handler.run(&Message {}).unwrap());
}