Macro dummy_args 

macro_rules! dummy_args {
    (
        $arg:ident $(,$tail:ident)* $(,)?
    ) => { ... };
    (
        unsafe $arg:ident $(,$tail:ident)* $(,)?
    ) => { ... };
    (
        $($unsafe:ident)?
        [$($t:tt)*]
        $arg:ident $($tail:ident)*
    ) => { ... };
    (
        $($unsafe:ident)?
        [$($t:tt)*]
    ) => { ... };
}