Macro param_count_match 

macro_rules! param_count_match {
    (
        [$($arg:ident),*]
        []
    ) => { ... };
    (
        [$($arg:ident),*]
        [$($sel:tt)*]
    ) => { ... };
    (
        [$arg1:ident $(,$tail1:ident)* $(,)?]
        [$sel:ident : $($tail2:ident :)*]
        [$($t:tt)*]
    ) => { ... };
    (
        [$arg1:ident, $arg2:ident]
        [$($sel:ident)?]
        [$($t:tt)*]
    ) => { ... };
    (
        [$($arg:tt)*]
        [$($sel:tt)*]
        [$($t:tt)*]
    ) => { ... };
}