返回指向成员函数的指针（没有typedef）

Question

Compiling on C++03, I've attempted to write up a test template function that returns a pointer-to-member-function of a member function that returns int, and takes two float arguments:

template<typename TemplateClass>
int (TemplateClass::*)(float,float) Testtest(TemplateClass &A)
{
    return &TemplateClass::Function;
}

But naturally, no matter what variations on the pointer-to-member-function syntax I use, the compiler complains of initialisation errors. Typedef, although it works with known classes, for obvious reasons (naming conflicts), won't accept template class arguments for classes that I can't know ahead of time which are likely to use the same function.

What non-typedef way is there to get this function to compile and return a pointer-to-member-function?

Answer 1

To declare it without a type alias, without type deduction, and without a trailing return type:

template<typename TemplateClass>
int (TemplateClass::* Testtest(TemplateClass &A))(float,float)

But of course this isn't what you would use in real code. Instead you would use an alias template :

template<typename T>
using return_type = int (T::*)(float,float);

template<typename TemplateClass>
return_type<TemplateClass> Testtest(TemplateClass &A)

Or return type deduction in C++14:

template<typename TemplateClass>
auto Testtest(TemplateClass &A)

Or a trailing return type (in C++11):

template<typename TemplateClass>
auto Testtest(TemplateClass &A) -> int (TemplateClass::*)(float,float)

Answer 2

You need this prototype:

template<typename TemplateClass>
int (TemplateClass::*Testtest(TemplateClass &A)) (float,float) { }

Answer 3

  int (Class::*f())(float,float);

f is function taking no arguments returning pointer to member function of class Class takinf 2 floats and returning int.

And template version:

         template <typename Type>
         int (Type::*f())(float,float);

Answer 4

I reject the premise of your question. Use typedefs. Or, specifically, a type trait:

template <class T, class F>
struct make_mem_fun {
    typedef F T::*type;
};

template<typename TemplateClass>
typename make_mem_fun<TemplateClass, int(float, float)>::type
Testtest(TemplateClass &A)
{
    return &TemplateClass::Function;
}

That is way easier to understand than the convoluted syntax of actually returning the type. With C++11, we can turn that into an alias to drop the typename ::type stuff.