epoc32/include/stdapis/boost/pending/ct_if.hpp
author William Roberts <williamr@symbian.org>
Tue, 16 Mar 2010 16:12:26 +0000
branchSymbian2
changeset 2 2fe1408b6811
permissions -rw-r--r--
Final list of Symbian^2 public API header files
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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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