trait Convert<'a, T: 'a> {
    fn convert(&self) -> Option<T>;
}

struct MyStruct;
impl<'a> Convert<'a, bool> for MyStruct {
    fn convert(&self) -> Option<bool> {
        Some(true)
    }
}

impl<'a> Convert<'a, usize> for MyStruct {
    fn convert(&self) -> Option<usize> {
        Some(1)
    }
}

fn main() {
    if let Some(_) = Convert::<usize>::convert(&MyStruct) {

    }
}