1 // (C) Copyright Jeremy Siek 2000.
2 // Distributed under the Boost Software License, Version 1.0. (See
3 // accompanying file LICENSE_1_0.txt or copy at
4 // http://www.boost.org/LICENSE_1_0.txt)
6 // The ct_if implementation that avoids partial specialization is
7 // based on the IF class by Ulrich W. Eisenecker and Krzysztof
10 #ifndef BOOST_CT_IF_HPP
11 #define BOOST_CT_IF_HPP
13 #include <boost/config.hpp>
16 There is a bug in the Borland compiler with regards to using
17 integers to specialize templates. This made it hard to use ct_if in
18 the graph library. Changing from 'ct_if' to 'ct_if_t' fixed the
22 #include <boost/type_traits/integral_constant.hpp> // true_type and false_type
26 struct ct_if_error { };
28 template <class A, class B>
29 struct ct_and { typedef false_type type; };
30 template <> struct ct_and<true_type,true_type> { typedef true_type type; };
32 template <class A> struct ct_not { typedef ct_if_error type; };
33 template <> struct ct_not<true_type> { typedef false_type type; };
34 template <> struct ct_not<false_type> { typedef true_type type; };
36 #ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
38 // agurt, 15/sep/02: in certain cases Borland has problems with
39 // choosing the right 'ct_if' specialization even though 'cond'
40 // _does_ equal '1'; the easiest way to fix it is to make first
41 // 'ct_if' non-type template parameter boolean.
42 #if !defined(__BORLANDC__)
43 template <bool cond, class A, class B>
44 struct ct_if { typedef ct_if_error type; };
45 template <class A, class B>
46 struct ct_if<true, A, B> { typedef A type; };
47 template <class A, class B>
48 struct ct_if<false, A, B> { typedef B type; };
50 template <bool cond, class A, class B>
51 struct ct_if { typedef A type; };
52 template <class A, class B>
53 struct ct_if<false, A, B> { typedef B type; };
56 template <class cond, class A, class B>
57 struct ct_if_t { typedef ct_if_error type; };
58 template <class A, class B>
59 struct ct_if_t<true_type, A, B> { typedef A type; };
60 template <class A, class B>
61 struct ct_if_t<false_type, A, B> { typedef B type; };
67 template <int condition, class A, class B> struct IF;
68 template <int condition> struct SlectSelector;
69 struct SelectFirstType;
70 struct SelectSecondType;
72 struct SelectFirstType {
73 template<class A, class B>
74 struct Template { typedef A type; };
77 struct SelectSecondType {
78 template<class A, class B>
79 struct Template { typedef B type; };
82 template<int condition>
83 struct SlectSelector {
84 typedef SelectFirstType type;
88 struct SlectSelector<0> {
89 typedef SelectSecondType type;
94 template<int condition, class A, class B>
97 typedef typename detail::SlectSelector<condition>::type Selector;
98 typedef typename Selector::template Template<A, B>::type type;
101 template <class cond, class A, class B>
103 typedef typename ct_if<cond::value, A, B>::type type;
110 #endif // BOOST_CT_IF_HPP