Rust with macro

macro_rules! with_key {
    ($($t:ty),+) => ($(
        impl WithKey for $t {
            fn key(&self) -> &str {
                &self.key
            }
        }
    )+);
}

#[derive(Debug)]
struct A {
    key: String,
    min: u8
}

// T because there can be another structure eg. B with 'key'
#[derive(Debug)]
struct Aggregation<T> {
    collection: Vec<T> 
}

trait WithKey {
    fn key(&self) -> &str;
    fn has_key(&self, value: &str) -> bool {
        self.key() == value
    }
}

with_key! { A }

impl<T:WithKey> Aggregation<T> {
    fn find_by_key(&self, value: String) -> &T {
        self.collection.iter().find(|t| t.has_key(&value)).unwrap()
    }
}

fn main() {
    let a = A{ key: "key1".to_string(), min: 1 };
    let b = A{ key: "key2".to_string(), min: 2 };
    let collection = vec!(a,b);
    
    let aggr = Aggregation { collection: collection };
    
    let res = aggr.find_by_key("key2".to_string());
    println!("{:?}", res);
}