C++ template errors

I'm trying out an implementation of a simple property system for C++ which I found here.

But the code won't compile.

template <class T, class Object, typename T (Object::*real_getter)()>
class ReadOnlyProperty
{
    Object * my_object;
public:
    void operator () ( Object * obj )
    {
        my_object = obj;
    }

    T operator()() const
    {
        return (my_object->real_getter)();
    }


    T get() const
    {
        return (my_object->real_getter)();
    }


    void set( T const & value );


    operator T() const {
        return (my_object->*real_getter)();
    }

    typedef T value_type;

};

I get multiple errors at the very first line. I'm using Xcode 4 and neither LLVM 2.1 or GCC 4.2 can compile this. What's the problem?

A member function pointer CAN be a template parameter, but in that case you should not put typename before:

template <class T, class Object, T (Object::*real_getter)()>

The other error is the call:

(my_object->real_getter)()

which should be:

(my_object->*real_getter)()

The template parameter list doesn't work like that. Template parameters must be one of: type names, types (with restrictions), or templates.

Maybe you mean to have a default type, like so?

template <class T,
          class Object,
          typename U = T (Object::*real_getter)()>
class ...

Here U defaults to a pointer-to-member-function, but you have to provide the complete signature including return type.

Or do you mean for real_getter to be a member typedef?

template <class T, class Object>
class ReadOnlyProperty
{
  typedef typename  T (Object::*real_getter)();
  //...
};

Or as @jmihalicza suggests, you want a value parameter of type T (Object::*)()?

template <class T, class Object, T (Object::*real_getter)()>
class ReadOnlyProperty
{ //...
};