How do I remove code duplication between similar const and non-const member functions?

Question

Let\'s say I have the following class X where I want to return access to an internal member:

class Z
{
    // details
};

class X
{
    std::vec         


        

Answer 1

I think Scott Meyers' solution can be improved in C++11 by using a tempate helper function. This makes the intent much more obvious and can be reused for many other getters.

template 
struct NonConst {typedef T type;};
template 
struct NonConst {typedef T type;}; //by value
template 
struct NonConst {typedef T& type;}; //by reference
template 
struct NonConst {typedef T* type;}; //by pointer
template 
struct NonConst {typedef T&& type;}; //by rvalue-reference

template
typename NonConst::type likeConstVersion(
   TObj const* obj,
   TConstReturn (TObj::* memFun)(TArgs...) const,
   TArgs&&... args) {
      return const_cast::type>(
         (obj->*memFun)(std::forward(args)...));
}

This helper function can be used the following way.

struct T {
   int arr[100];

   int const& getElement(size_t i) const{
      return arr[i];
   }

   int& getElement(size_t i) {
      return likeConstVersion(this, &T::getElement, i);
   }
};

The first argument is always the this-pointer. The second is the pointer to the member function to call. After that an arbitrary amount of additional arguments can be passed so that they can be forwarded to the function. This needs C++11 because of the variadic templates.