Macro to_tokens 

macro_rules! to_tokens {
    (
        $(#[$struct_attr:meta])*
        $struct_vis:vis struct $struct_name:ident {$(
            $(#[$field_attr:meta])*
            $field_vis:vis $field_name:ident : $field_ty:ty = $default:pat
        ),* $(,)?}
    ) => { ... };
    (
        $(#[$enum_attr:meta])*
        $enum_vis:vis enum $enum_name:ident {$(
            $(#[$variant_attr:meta])*
            $variant_name:ident
        ),+ $(,)?}
    ) => { ... };
}