Map a named struct to enum entries.

lib.rs

macro_rules! collection {
    (enum $enum_name:ident {$($variant_name:ident {$($field_name:ident: $field_type:ty$(,)*)*},)+}) => {
        $(struct $variant_name {
            $($field_name: $field_type,)*
        })+

        enum $enum_name {
            $($variant_name($variant_name),)+
        }
    }
}

////////////////////////////////

collection!{
    enum Action {
        Walking {},
        Running {speed: i32},
    }
}

fn main() {
    Action::Walking(Walking{});
    Action::Running(Running{speed:123});
}