Re: [Boost-users] compile-time check that a member function exists

From: Joel FALCOU (joel.falcou_at_[hidden])
Date: 2008-07-22 15:35:38

John Pretz a écrit :
> Hi,
>
> I'm pretty new to boost.  I want to write some code with a 
> compile-time check whether a member function exists or not.  The code 
> below shows kinda what I need except I'd obviously like to avoid a 
> specialized template for each class that I use.
>
> Can anybody point me in the right direction?
>
Not sure if it exists in boost, but the good old trick using the (...) 
operator may be enough.
Like :

typedef char NotFound; 
struct Found { char x[2]; };

template <class T, void  (T::*)() const > struct test_for_member_go{ };
template<class T> static Found       
test_for_go(test_for_member_go<T,&T::go>*);
template<class T> static NotFound test_for_go( ... );

template<class T>
struct test
{
   static const bool value = (sizeof( test_for_go<T>( 0 ) ) == 
sizeof(Found));
  typedef boost::mpl::bool_<value> type;
};

then test<X>::type should give you a CT boolean that indicates if go is 
a member of T.
This could be easily turned into a macro-like features that can be 
retargeted for any member with any signature.

-- 
Joel FALCOU
Research Engineer @ Institut d'Electronique Fondamentale
Université PARIS SUD XI
France