Macro coercion::unsafe_impl_coerce

macro_rules! unsafe_impl_coerce {
    ( $t:ty => $u:ty ) => { ... };
    ( $t:ty | $u:ty ) => { ... };
    ( $t:ty | $u:ty | $( $u_remaining:ty )|+ ) => { ... };
    ( $( { $t:ty | $( $u:ty )|+ }; )+ ) => { ... };
}

Implements Coerce for sized types.