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