Re: const/non const member function vs. templates

Stuart Redmann <>
Fri, 29 Jul 2011 02:58:14 -0700 (PDT)
On 26 Jul., 14:58, Markus Keppeler <> wrote:

Hi Together!

In some (partly legacy) code I have member functions like this:

// class Dummy (class of any type).
class XY
   Dummy *pGetMe( (returns pointer to some
   ); dummy member orw=


   const Dummy *pGetMe( (returns const pointer to some
   ) const; dummy member or whatev=



Since the implementations on both pGetMe's are 100% identically, only
that they use const/non const types/functions, I'd like to merge them.

I cannot implement the non-const version by calling down to the const
one, since at some level it needs to fetch the non-const pointer to
something. Here also some legacy-issues come into, so I cannot
refactor the entire design ;-).

My next thought was to use templates, like

   template <class T>
   T pGetMe();

, but here I don't know how to deal with the const/non constness of
the member function. Can I add the const/non const based on the type
of T?

The following is not exactly what you want but it comes quite close:

// Wrapper for plain pointers that behaves as const-correct
// accessor.
template<class t_Class>
class ConstCorrectAccessor
  t_Class* m_InternalPointer;
  ConstCorrectAccessor (t_Class* Pointer)
    : m_InternalPointer (Pointer)

  // Accessor methods with const-correct overload.
  const t_Class* operator-> () const {return m_InternalPointer;}
  t_Class* operator ->() {return m_InternalPointer;}

  const t_Class* operator& () const {return m_InternalPointer;}
  t_Class* operator& () {return m_InternalPointer;}

class Dummy;

class XY
  ConstCorrectAccessor<Dummy> Me;

void foo (const XY& xy)
  const Dummy* OK = &xy.Me;
  Dummy* DOES_NOT_COMPILE = &xy.Me;

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