sl@0: // (C) Copyright Jeremy Siek 2000.
sl@0: // Distributed under the Boost Software License, Version 1.0. (See
sl@0: // accompanying file LICENSE_1_0.txt or copy at
sl@0: // http://www.boost.org/LICENSE_1_0.txt)
sl@0: 
sl@0: // The ct_if implementation that avoids partial specialization is
sl@0: // based on the IF class by Ulrich W. Eisenecker and Krzysztof
sl@0: // Czarnecki.
sl@0: 
sl@0: #ifndef BOOST_CT_IF_HPP
sl@0: #define BOOST_CT_IF_HPP
sl@0: 
sl@0: #include <boost/config.hpp>
sl@0: 
sl@0: /*
sl@0:   There is a bug in the Borland compiler with regards to using
sl@0:   integers to specialize templates. This made it hard to use ct_if in
sl@0:   the graph library. Changing from 'ct_if' to 'ct_if_t' fixed the
sl@0:   problem.
sl@0: */
sl@0: 
sl@0: #include <boost/type_traits/integral_constant.hpp> // true_type and false_type
sl@0: 
sl@0: namespace boost {
sl@0: 
sl@0:   struct ct_if_error { };
sl@0: 
sl@0:   template <class A, class B>
sl@0:   struct ct_and { typedef false_type type; };
sl@0:   template <> struct ct_and<true_type,true_type> { typedef true_type type; };
sl@0: 
sl@0:   template <class A> struct ct_not { typedef ct_if_error type; };
sl@0:   template <> struct ct_not<true_type> { typedef false_type type; };
sl@0:   template <> struct ct_not<false_type> { typedef true_type type; };
sl@0: 
sl@0: #ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
sl@0: 
sl@0: // agurt, 15/sep/02: in certain cases Borland has problems with
sl@0: // choosing the right 'ct_if' specialization even though 'cond' 
sl@0: // _does_ equal '1'; the easiest way to fix it is to make first 
sl@0: // 'ct_if' non-type template parameter boolean.
sl@0: #if !defined(__BORLANDC__)
sl@0:   template <bool cond, class A, class B>
sl@0:   struct ct_if { typedef ct_if_error type; };
sl@0:   template <class A, class B>
sl@0:   struct ct_if<true, A, B> { typedef A type; };
sl@0:   template <class A, class B>
sl@0:   struct ct_if<false, A, B> { typedef B type; };
sl@0: #else
sl@0:   template <bool cond, class A, class B>
sl@0:   struct ct_if { typedef A type; };
sl@0:   template <class A, class B>
sl@0:   struct ct_if<false, A, B> { typedef B type; };
sl@0: #endif
sl@0: 
sl@0:   template <class cond, class A, class B>
sl@0:   struct ct_if_t { typedef ct_if_error type; };
sl@0:   template <class A, class B>
sl@0:   struct ct_if_t<true_type, A, B> { typedef A type; };
sl@0:   template <class A, class B>
sl@0:   struct ct_if_t<false_type, A, B> { typedef B type; };
sl@0: 
sl@0: #else
sl@0: 
sl@0:   namespace detail {
sl@0: 
sl@0:     template <int condition, class A, class B> struct IF;
sl@0:     template <int condition> struct SlectSelector;
sl@0:     struct SelectFirstType;
sl@0:     struct SelectSecondType;
sl@0:     
sl@0:     struct SelectFirstType {
sl@0:       template<class A, class B>
sl@0:       struct Template {        typedef A type; };
sl@0:     };
sl@0:     
sl@0:     struct SelectSecondType {
sl@0:       template<class A, class B>
sl@0:       struct Template { typedef B type; };
sl@0:     };
sl@0:     
sl@0:     template<int condition>
sl@0:     struct SlectSelector {
sl@0:       typedef SelectFirstType type;
sl@0:     };
sl@0:     
sl@0:     template <>
sl@0:     struct SlectSelector<0> {
sl@0:       typedef SelectSecondType type;
sl@0:     };
sl@0: 
sl@0:   } // namespace detail
sl@0:     
sl@0:   template<int condition, class A, class B>
sl@0:   struct ct_if
sl@0:   {
sl@0:     typedef typename detail::SlectSelector<condition>::type Selector;
sl@0:     typedef typename Selector::template Template<A, B>::type type;
sl@0:   };
sl@0:   
sl@0:   template <class cond, class A, class B>
sl@0:   struct ct_if_t { 
sl@0:     typedef typename ct_if<cond::value, A, B>::type type;
sl@0:   };
sl@0: 
sl@0: #endif
sl@0: 
sl@0: } // namespace boost
sl@0: 
sl@0: #endif // BOOST_CT_IF_HPP
sl@0: