Specialization-based approach to an AnyMap-like structure

anymap_spec.rs

#![feature(specialization)]
#![allow(dead_code)]

struct Nil;
struct Cons<H, T>(H, T);

trait MayContain<T> {
    fn get(&self) -> Option<&T>;
    fn get_mut(&mut self) -> Option<&mut T>;
}

impl<T> MayContain<T> for Nil {
    fn get(&self) -> Option<&T> {
        None
    }
    fn get_mut(&mut self) -> Option<&mut T> {
        None
    }
}

impl<T, Tail: MayContain<T>> MayContain<T> for Cons<T, Tail> {
    fn get(&self) -> Option<&T> {
        Some(&self.0)
    }
    fn get_mut(&mut self) -> Option<&mut T> {
        Some(&mut self.0)
    }
}

impl<T, Head, Tail: MayContain<T>> MayContain<T> for Cons<Head, Tail> {
    default fn get(&self) -> Option<&T> {
        self.1.get()
    }
    default fn get_mut(&mut self) -> Option<&mut T> {
        self.1.get_mut()
    }
}

fn main() {
    fn show_i32<T: MayContain<i32>>(t: &T) {
        println!("{:?}", t.get());
    }
    let list1 = Cons(1i32, Cons(2i64, Cons("", Nil)));
    let list2 = Cons(1i64, Cons(2i32, Cons("", Nil)));
    let list3 = Cons(1i64, Cons("", Cons(3i32, Nil)));
    let list4 = Cons(4i32, Cons("", Cons(3i32, Nil)));
    let list5 = Cons(0i64, Cons("", Cons(1i64, Nil)));
    show_i32(&list1);
    show_i32(&list2);
    show_i32(&list3);
    show_i32(&list4);
    show_i32(&list5);

    
}