Re: The CRTP pattern and member function pointer template parameter

From:

Carl Barron <cbarron413@adelphia.net>

Newsgroups:

comp.lang.c++.moderated

Date:

Thu, 28 Jun 2007 03:36:01 CST

Message-ID:

<280620070127194106%cbarron413@adelphia.net>

In article <1182980794.303806.163550@k79g2000hse.googlegroups.com>,
Olivier Langlois <olanglois@sympatico.ca> wrote:

Hi,

I wanted to achieve static polymorphism with the CRTP pattern to
create a base class for encapsulating the thread creation with the
pthread API. What I was trying was:

template<class D, void *(D::*F)()>
class ThreadBase
{
static void *start_routine(void *arg);
};

template<class D, void *(D::*F)()>
void *ThreadBase<D,F>::start_routine(void *arg)
{
    D *pThis = static_cast<D *>(arg);
    return (pThis->*F)();
}

where I could have defined a derived class:

class Derived : public ThreadBase<Derived,&Derived::Run>
{
    void *Run();
};

but it does not work. GCC complains that:

incomplete type `Derived' used in nested name specifier.

Right now, I am blinded with my initial design that does not work so I
would like to ask this newsgroup readers for suggestions about the
best way solve my problem.

GCC 3.x compiles this just fine;
template<class D>
struct ThreadBase
{
   typedef void *(D::*PMF)();
   void *start_routine(PMF x)
   {
      D *p = static_cast<D *>(this);
      return (p->*x)();
   }
};

struct Derived:ThreadBase<Derived>
{
   void *run();
};

inline void test()
{
   Derived p;
   p.start_routine(&Derived::run);
}

should be as useful as you thought you were getting, in that the
call is hardcoded but not ThreadBase,

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