David Abrahams wrote:
"Suki" <suryakiran.gullapalli@gmail.com> writes:
Hi, I'm writing a templated class, and i dont want to use the class otherthan for some predetermined types, say, int, double etc.
This class has no meaning for typenames other than those few.
========================= template <class T> myClass {....} ;
myClass<int> intClass ; myClass<float> floatClass ; myClass<char> charClass ; =========================
The compiler should not complain for the first 2 instantiations, but should bail out at the 3rd instantiation (charClass). Is there any way i can achieve this, using standard c++ or boost.
Declarative way:
template <class T> struct myClass_impl { ... };
template <class T> struct myClass;
template<> myClass<int> : myClass_impl<int> {};
template<> myClass<float> : myClass_impl<float> {};
template<> myClass<char> : myClass_impl<char> {};
you mean 'struct myClass<foo> : public myClass_impl<foo>', I assume?
Imperative way:
#include <boost/mpl/or.hpp> #include <boost/mpl/assert.hpp> #include <boost/type_traits/is_same.hpp>
template <class T> struct myClass { BOOST_MPL_ASSERT((boost::mpl::or_< boost::is_same<T,int> , boost::is_same<T,float> , boost::is_same<T,char> >));
... // your class implementation here. };
This would slow down compile times a bit, though, would it not? (but give better error messages!) Not that it matters much. Where's the functional way? :-D (Don't answer that) Perhaps abstracting the check to a traits class would be helpful? Depends on what it's for, I guess. -- don't quote this