83 lines
2.4 KiB
Plaintext
83 lines
2.4 KiB
Plaintext
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// Copyright Daniel Wallin 2006. Use, modification and distribution is
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// subject to the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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#ifndef BOOST_PARAMETER_VALUE_TYPE_060921_HPP
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# define BOOST_PARAMETER_VALUE_TYPE_060921_HPP
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# include <boost/mpl/apply.hpp>
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# include <boost/mpl/assert.hpp>
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# include <boost/mpl/and.hpp>
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# include <boost/parameter/aux_/result_of0.hpp>
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# include <boost/parameter/aux_/void.hpp>
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# include <boost/type_traits/is_same.hpp>
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namespace boost { namespace parameter {
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// A metafunction that, given an argument pack, returns the type of
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// the parameter identified by the given keyword. If no such
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// parameter has been specified, returns Default
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# if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
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template <class Parameters, class Keyword, class Default>
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struct value_type0
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{
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typedef typename mpl::apply_wrap3<
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typename Parameters::binding,Keyword,Default,mpl::false_
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>::type type;
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BOOST_MPL_ASSERT_NOT((
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mpl::and_<
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is_same<Default, void_>
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, is_same<type, void_>
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>
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));
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};
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# endif
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template <class Parameters, class Keyword, class Default = void_>
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struct value_type
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{
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# if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
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typedef typename mpl::eval_if<
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mpl::is_placeholder<Parameters>
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, mpl::identity<int>
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, value_type0<Parameters,Keyword,Default>
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>::type type;
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# else
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typedef typename mpl::apply_wrap3<
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typename Parameters::binding,Keyword,Default,mpl::false_
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>::type type;
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BOOST_MPL_ASSERT_NOT((
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mpl::and_<
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is_same<Default, void_>
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, is_same<type, void_>
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>
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));
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# endif
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BOOST_MPL_AUX_LAMBDA_SUPPORT(3,value_type,(Parameters,Keyword,Default))
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};
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// A metafunction that, given an argument pack, returns the type of
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// the parameter identified by the given keyword. If no such
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// parameter has been specified, returns the type returned by invoking
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// DefaultFn
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template <class Parameters, class Keyword, class DefaultFn>
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struct lazy_value_type
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{
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typedef typename mpl::apply_wrap3<
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typename Parameters::binding
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, Keyword
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, typename aux::result_of0<DefaultFn>::type
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, mpl::false_
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>::type type;
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};
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}} // namespace boost::parameter
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#endif // BOOST_PARAMETER_VALUE_TYPE_060921_HPP
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