Re: [Boost-users] Templates Question

From: David Abrahams (dave_at_[hidden])
Date: 2005-10-27 07:01:54

"Suki" <suryakiran.gullapalli_at_[hidden]> 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>
  {};

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.
  };

> to summarize my question,
> is there any way i can restrict the compiler to accept only few type
> names for my templated class (i.e., using standard c++ or boost)

HTH,

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com