Macro gated 

macro_rules! gated {
    (unsafe $attr:ident, $gate:ident, $message:expr $(,)?) => { ... };
    (unsafe $attr:ident, $message:expr $(,)?) => { ... };
    ($attr:ident, $gate:ident, $message:expr $(,)?) => { ... };
    ($attr:ident, $message:expr $(,)?) => { ... };
}