Macro internal_impl_enum_from 

macro_rules! internal_impl_enum_from {
    (
            $enum_name:ident,
            $member:ident($inner_type1:ty, $($inner_type2:ty),+)
        ) => { ... };
    (
            $enum_name:ident,
            $member:ident($inner_type:ty)
        ) => { ... };
}

For internal use only.