downcast-rs 1.1.1

Trait object downcasting support using only safe Rust. It supports type parameters, associated types, and type constraints.
Documentation 
#[macro_use]
extern crate downcast_rs;

#[test]
fn test() {
    use downcast_rs::Downcast;
    trait Trait: Downcast {}
    impl_downcast!(Trait);
}