[boost] How to cast _1 ?

I want to cast a value of _1 to a _val of a different type. How do I do that? I tried using static_cast_, it does not compile for me. rule<UInt8Iterator, UInt32()> MyRule; ... MyRule = (long_ | float_) [_val = static_cast_<UInt32>(_1)] Any help is appreciated Regards, Henry