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Replaced the implementation of ct_if with a facade implementation that

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defers to Boost.MPL.


[SVN r36022]
This commit is contained in:
Ronald Garcia
2006-11-13 15:35:54 +00:00
parent 4e009de1ec
commit a548ecc968
1 changed files with 18 additions and 86 deletions
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104
include/boost/pending/ct_if.hpp
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@ -3,107 +3,39 @@
// accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
// The ct_if implementation that avoids partial specialization is
// based on the IF class by Ulrich W. Eisenecker and Krzysztof
// Czarnecki.
// This header replaces the implementation of ct_if that preceded the
// introduction of Boost.MPL with a facade that defers to that reviewed and
// accepted library.
// Author: Ronald Garcia
// Date: 20 October, 2006
#ifndef BOOST_CT_IF_HPP
#define BOOST_CT_IF_HPP
#include <boost/config.hpp>
/*
There is a bug in the Borland compiler with regards to using
integers to specialize templates. This made it hard to use ct_if in
the graph library. Changing from 'ct_if' to 'ct_if_t' fixed the
problem.
*/
// A stub implementation in terms of Boost.MPL
#include <boost/type_traits/integral_constant.hpp> // true_type and false_type
#include <boost/mpl/if.hpp>
#include <boost/mpl/not.hpp>
#include <boost/mpl/and.hpp>
// true_type and false_type are used by applications of ct_if
#include <boost/type_traits/integral_constant.hpp>
namespace boost {
struct ct_if_error { };
template <class A, class B>
struct ct_and { typedef false_type type; };
template <> struct ct_and<true_type,true_type> { typedef true_type type; };
struct ct_and : boost::mpl::and_<A,B> {};
template <class A> struct ct_not { typedef ct_if_error type; };
template <> struct ct_not<true_type> { typedef false_type type; };
template <> struct ct_not<false_type> { typedef true_type type; };
template <class A>
struct ct_not : mpl::not_<A> {};
#ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
// agurt, 15/sep/02: in certain cases Borland has problems with
// choosing the right 'ct_if' specialization even though 'cond'
// _does_ equal '1'; the easiest way to fix it is to make first
// 'ct_if' non-type template parameter boolean.
#if !defined(__BORLANDC__)
template <bool cond, class A, class B>
struct ct_if { typedef ct_if_error type; };
template <class A, class B>
struct ct_if<true, A, B> { typedef A type; };
template <class A, class B>
struct ct_if<false, A, B> { typedef B type; };
#else
template <bool cond, class A, class B>
struct ct_if { typedef A type; };
template <class A, class B>
struct ct_if<false, A, B> { typedef B type; };
#endif
struct ct_if : mpl::if_c<cond,A,B> {};
template <class cond, class A, class B>
struct ct_if_t { typedef ct_if_error type; };
template <class A, class B>
struct ct_if_t<true_type, A, B> { typedef A type; };
template <class A, class B>
struct ct_if_t<false_type, A, B> { typedef B type; };
#else
namespace detail {
template <int condition, class A, class B> struct IF;
template <int condition> struct SlectSelector;
struct SelectFirstType;
struct SelectSecondType;
struct SelectFirstType {
template<class A, class B>
struct Template { typedef A type; };
};
struct SelectSecondType {
template<class A, class B>
struct Template { typedef B type; };
};
template<int condition>
struct SlectSelector {
typedef SelectFirstType type;
};
template <>
struct SlectSelector<0> {
typedef SelectSecondType type;
};
} // namespace detail
template<int condition, class A, class B>
struct ct_if
{
typedef typename detail::SlectSelector<condition>::type Selector;
typedef typename Selector::template Template<A, B>::type type;
};
template <class cond, class A, class B>
struct ct_if_t {
typedef typename ct_if<cond::value, A, B>::type type;
};
#endif
struct ct_if_t : mpl::if_<cond,A,B> {};
} // namespace boost