Re: [Boost-users] Templates Question

David Abrahams wrote:

"Suki" 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 #include #include

template <class T> struct myClass { BOOST_MPL_ASSERT((boost::mpl::or_< boost::is_same , boost::is_same , boost::is_same >));

... // 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