Switched Return

Essentially what I am liking to do here is make a templated function call where the caller essentially requests a given type and either a pointer or a reference will be passed back. Based on the type given in the template I wish to return the retrieved unadjusted pointer if it is a pointer and if it is a stored value I would like to switch type to reference. I would also like to expand this thought to include references, classes, pointers to classes and so on ...

#include <utility>
#include <type_traits>
using namespace std;
using namespace std::tr1;

template< bool condition, typename Then, typename Else >
struct IF {
    typedef typename Then RET;
};
template<typename Then, typename Else >
struct IF< false, Then, Else > {
    typedef typename Else RET;
};

template<class T>
struct ReturnType {

    typedef typename IF<std::is_pointer<T>::value, T, T& >::RET RET;

};

template<bool condition, typename U>
struct Member {
    Member(){ value = 2; member = &value; };
    int value;
    int* member;
};
temp开发者_运维知识库late<typename U>
struct Member<false, U> {
    Member(){ member = 5; };
    int member;
};

typedef class tagFOO {
public:

    template < typename T >
    typename ReturnType<T>::RET function()
    {
        Member<std::is_pointer<T>::value, T> ret;

        return ret.member;
    };

} FOO;


int main() {

    int i = 0;
    int* pi = NULL;

    FOO A;

    i = A.function<int>();
    pi = A.function<int*>();

    return 0;
}

This code when ran outputs 5 and 2 respectively.

I guess my first issue with doing this was with defining the return type where I would have liked to have done this

auto function()->decltype(typename ReturnType<T>::RET)

instead. I'm not sure why this doesn't work I just get an unresolved template error in any combination of everything I could possibly imagine.

My second issue is in handling a variety of different return types. This is going to be a bit trialing and, correct me if I'm wrong, a trailing return type would be a quick fix because the compiler seems to ignore the invalid returns. This was something I tested by simply passing ->decltype(T) but I may have made a mistake in my test somewhere.

I think what I have here will be enough to get the job done. I'm sure there are a few opinions on why this might not be such a great idea and I would love to hear those.

thx, BekaD:

---

Maybe boost::call_traits can help.

http://boost.org/doc/libs/1_45_0/libs/utility/call_traits.htm