Macro coercion::unsafe_impl_as

macro_rules! unsafe_impl_as {
    ( $src:ty => $( $dst:ty ),+ ) => { ... };
    ($src:ty = $dst:ty ) => { ... };
    ($src:ty = $dst:ty $(= $rest:ty )+ ) => { ... };
    ({ $src:ty => $( $dst:ty ),+ }) => { ... };
    ({ $src:ty = $( $dst:ty )=+ }) => { ... };
    ( $( $def:tt; )+ ) => { ... };
}

Implements As for a sized types.