williamr@2: // (C) Copyright Jeremy Siek 2000.
williamr@2: // Distributed under the Boost Software License, Version 1.0. (See
williamr@2: // accompanying file LICENSE_1_0.txt or copy at
williamr@2: // http://www.boost.org/LICENSE_1_0.txt)
williamr@2: 
williamr@2: // The ct_if implementation that avoids partial specialization is
williamr@2: // based on the IF class by Ulrich W. Eisenecker and Krzysztof
williamr@2: // Czarnecki.
williamr@2: 
williamr@2: #ifndef BOOST_CT_IF_HPP
williamr@2: #define BOOST_CT_IF_HPP
williamr@2: 
williamr@2: #include <boost/config.hpp>
williamr@2: 
williamr@2: /*
williamr@2:   There is a bug in the Borland compiler with regards to using
williamr@2:   integers to specialize templates. This made it hard to use ct_if in
williamr@2:   the graph library. Changing from 'ct_if' to 'ct_if_t' fixed the
williamr@2:   problem.
williamr@2: */
williamr@2: 
williamr@2: #include <boost/type_traits/integral_constant.hpp> // true_type and false_type
williamr@2: 
williamr@2: namespace boost {
williamr@2: 
williamr@2:   struct ct_if_error { };
williamr@2: 
williamr@2:   template <class A, class B>
williamr@2:   struct ct_and { typedef false_type type; };
williamr@2:   template <> struct ct_and<true_type,true_type> { typedef true_type type; };
williamr@2: 
williamr@2:   template <class A> struct ct_not { typedef ct_if_error type; };
williamr@2:   template <> struct ct_not<true_type> { typedef false_type type; };
williamr@2:   template <> struct ct_not<false_type> { typedef true_type type; };
williamr@2: 
williamr@2: #ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
williamr@2: 
williamr@2: // agurt, 15/sep/02: in certain cases Borland has problems with
williamr@2: // choosing the right 'ct_if' specialization even though 'cond' 
williamr@2: // _does_ equal '1'; the easiest way to fix it is to make first 
williamr@2: // 'ct_if' non-type template parameter boolean.
williamr@2: #if !defined(__BORLANDC__)
williamr@2:   template <bool cond, class A, class B>
williamr@2:   struct ct_if { typedef ct_if_error type; };
williamr@2:   template <class A, class B>
williamr@2:   struct ct_if<true, A, B> { typedef A type; };
williamr@2:   template <class A, class B>
williamr@2:   struct ct_if<false, A, B> { typedef B type; };
williamr@2: #else
williamr@2:   template <bool cond, class A, class B>
williamr@2:   struct ct_if { typedef A type; };
williamr@2:   template <class A, class B>
williamr@2:   struct ct_if<false, A, B> { typedef B type; };
williamr@2: #endif
williamr@2: 
williamr@2:   template <class cond, class A, class B>
williamr@2:   struct ct_if_t { typedef ct_if_error type; };
williamr@2:   template <class A, class B>
williamr@2:   struct ct_if_t<true_type, A, B> { typedef A type; };
williamr@2:   template <class A, class B>
williamr@2:   struct ct_if_t<false_type, A, B> { typedef B type; };
williamr@2: 
williamr@2: #else
williamr@2: 
williamr@2:   namespace detail {
williamr@2: 
williamr@2:     template <int condition, class A, class B> struct IF;
williamr@2:     template <int condition> struct SlectSelector;
williamr@2:     struct SelectFirstType;
williamr@2:     struct SelectSecondType;
williamr@2:     
williamr@2:     struct SelectFirstType {
williamr@2:       template<class A, class B>
williamr@2:       struct Template {        typedef A type; };
williamr@2:     };
williamr@2:     
williamr@2:     struct SelectSecondType {
williamr@2:       template<class A, class B>
williamr@2:       struct Template { typedef B type; };
williamr@2:     };
williamr@2:     
williamr@2:     template<int condition>
williamr@2:     struct SlectSelector {
williamr@2:       typedef SelectFirstType type;
williamr@2:     };
williamr@2:     
williamr@2:     template <>
williamr@2:     struct SlectSelector<0> {
williamr@2:       typedef SelectSecondType type;
williamr@2:     };
williamr@2: 
williamr@2:   } // namespace detail
williamr@2:     
williamr@2:   template<int condition, class A, class B>
williamr@2:   struct ct_if
williamr@2:   {
williamr@2:     typedef typename detail::SlectSelector<condition>::type Selector;
williamr@2:     typedef typename Selector::template Template<A, B>::type type;
williamr@2:   };
williamr@2:   
williamr@2:   template <class cond, class A, class B>
williamr@2:   struct ct_if_t { 
williamr@2:     typedef typename ct_if<cond::value, A, B>::type type;
williamr@2:   };
williamr@2: 
williamr@2: #endif
williamr@2: 
williamr@2: } // namespace boost
williamr@2: 
williamr@2: #endif // BOOST_CT_IF_HPP
williamr@2: