I haven't used C++ in a long time but I've never seen or heard of this style of declaration. Especially since "union" is a reserved word in C.
Normally, functions are declared by stating their return type, followed by the name and the parameter list, plus the function body (the latter two is what makes them functions). There is no special keyword required, and the double arrow notation isn't a thing either. I'm only aware of a single arrow (to access members of a pointer) and the shift operator (>>), but of course C++ does allow you to overload operators and I believe even declare your own.
Normally, functions are declared by stating their return type, followed by the name and the parameter list, plus the function body (the latter two is what makes them functions). There is no special keyword required, and the double arrow notation isn't a thing either. I'm only aware of a single arrow (to access members of a pointer) and the shift operator (>>), but of course C++ does allow you to overload operators and I believe even declare your own.
