How to provide stl like container with public const iterator and private non-const iterator?

Programmer Question

Hello,

I have a class that includes a std::list and wish to provide public begin() and end() for const_iterator and private begin() and end() for just plain iterator.

However, the compiler is seeing the private version and complaining that it is private instead of using the public const version.

I understand that C++ will not overload on return type (in this case const_iterator and iterator) and thus it is choosing the non-const version since my object is not const.

Short of casting my object to const before calling begin() or not overloading the name begin is there a way to accomplish this?

I would think this is a known pattern that folks have solved before and would like to follow suit as to how this is typically solved.

class myObject {
public:
  void doSomethingConst() const;
};

class myContainer {
public:
  typedef std::list<myObject>::const_iterator const_iterator;
private:
  typedef std::list<myObject>::iterator iterator;

public:
  const_iterator begin() const { return _data.begin(); }
  const_iterator end()   const { return _data.end();   }
  void reorder();
private:
  iterator begin() { return _data.begin(); }
  iterator end()   { return _data.end();   }
private:
  std::list<myObject> _data;
};

void myFunction(myContainer &container) {
  myContainer::const_iterator itr = container.begin();
  myContainer::const_iterator endItr = container.end();
  for (; itr != endItr; ++itr) {
    const myObject &item = *itr;
    item.doSomethingConst();
  }
  container.reorder(); // Do something non-const on container itself.
}

The error from the compiler is something like this:

../../src/example.h:447: error: `std::_List_iterator<myObject> myContainer::begin()' is private
caller.cpp:2393: error: within this context
../../src/example.h:450: error: `std::_List_iterator<myObject> myContainer::end()' is private
caller.cpp:2394: error: within this context

Thanks.

-William

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