Macro lang_extension::as_boxed

macro_rules! as_boxed {
    ($trait:tt) => { ... };
    (impl $trait:tt) => { ... };
    (impl Hash for $trait:tt) => { ... };
    (impl PartialEq for $trait:tt) => { ... };
    (impl Eq for $trait:tt) => { ... };
    (impl Clone for $trait:tt) => { ... };
}