How to avoid code duplication implementing const and non-const iterators?

Question

I\'m implementing a custom container with an STL-like interface. I have to provide a regular iterator and a const iterator. Most of the code for the two versions of the it

Answer 1

You can use CRTP and a common base to "inject" methods (but you still have to duplicate ctors in current C++), or just use the preprocessor (no shuddering required; handles ctors easily):

struct Container {

#define G(This) \
This operator++(int) { This copy (*this); ++*this; return copy; }
// example of postfix++ delegating to ++prefix

  struct iterator : std::iterator<...> {
    iterator& operator++();
    G(iterator)
  };
  struct const_iterator : std::iterator<...> {
    const_iterator& operator++();
    G(const_iterator)
  };

#undef G
// G is "nicely" scoped and treated as an implementation detail
};

Use std::iterator, the typedefs it gives you, and any other typedefs you might provide to make the macro straight-forward.