Macro associated_fn

macro_rules! associated_fn {
    (fn drop(&mut self, $arg:ident: $arg_ty:ty)) => { ... };
    (fn clone(&mut self, $arg:ident: $arg_ty:ty) -> $ret_ty:ty) => { ... };
    ($($item:tt)*) => { ... };
}

🔬This is a nightly-only experimental API. (proc_macro_internals #27812)

Declare an associated fn of one of the traits below, adding necessary default bodies.