Re: [Boost-users] Enforcing CRTP with the MPL?

Gennadiy Rozental wrote:

"Stefan Schild" wrote in message news:eg3r7s$bcb$1@sea.gmane.org...

...

Hi there

Having a templatized base class B

template<class T> class B .....

is it possible to enforce that a class D can derive from B IF AND ONLY IF the curiously recurring template pattern is applied, that is

class D1 : public B<D1> ... // ok, compile class D2 : public B<X> ... // not ok, do not compile

???

Thx Stefan

Did you try:

template<typename T> class B { BOOST_STATIC_ASSERT( boost::is_base_and_derived::value ); .... };

This doesn't quite work? At this point, T is incomplete. But, it ought to be possible to put this check inside some member function of B; probably the one that casts *this to T& would be the ideal place. But then it should be pretty much unnecessary as the static_cast will fail if the conversion is not possible. Stefan, can you give more details, i.e. a *real* example where you want it to fail to compile, but it does? Cheers, Ian McCulloch