Macro default_macro::default

macro_rules! default {
    ( $name:ident { } ) => { ... };
    ( $name:ident { $field_name:tt : $value:tt $($tail:tt)* } ) => { ... };
    ( $name:expr ) => { ... };
    ( @x $name:ident {$($processed:tt)*} {$($current:tt)+} $(,)? ) => { ... };
    ( @x $name:ident {$($processed:tt)+} {$($current:tt)+} , $field_name:tt : $value:tt $($tail:tt)* ) => { ... };
    ( @x $name:ident {$($processed:tt)+} {$($current:tt)+} $value:tt $($tail:tt)*) => { ... };
}