Question

Consider the following example

template<class Type = void> class MyClass
{
    public:
        double getValue()
        {
            // if "Type == void" return _x, if "Type != void" return _y
            return (/* SOMETHING */) ? (_x) : (_y);
        }
    protected:
        double _x;
        static const double _y;
}; 

What could be the /* SOMETHING */ condition ?

I want to return _x if the template parameter is void, and return _y if not. How to do that ?

Answer 1

First off, you can’t return anything because the function return type is void.(fixed)

Second, you can specialize that function to act differently when Type is void:

template<class Type> class MyClass
{
    public:
        double getValue()
        {
            return _y;
        }
    protected:
        double _x;
        static const double _y;
}; 

template<>
inline double MyClass<void>::getValue()
{
   return _x;
}