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158 lines
4 KiB
C++
158 lines
4 KiB
C++
// Copyright David Abrahams 2003. 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 IS_LVALUE_ITERATOR_DWA2003112_HPP
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# define IS_LVALUE_ITERATOR_DWA2003112_HPP
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#include <boost/iterator.hpp>
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#include <boost/detail/workaround.hpp>
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#include <boost/detail/iterator.hpp>
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#include <boost/iterator/detail/any_conversion_eater.hpp>
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// should be the last #includes
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#include <boost/type_traits/detail/bool_trait_def.hpp>
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#include <boost/iterator/detail/config_def.hpp>
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#ifndef BOOST_NO_IS_CONVERTIBLE
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namespace boost {
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namespace iterators {
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namespace detail
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{
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#ifndef BOOST_NO_LVALUE_RETURN_DETECTION
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// Calling lvalue_preserver( <expression>, 0 ) returns a reference
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// to the expression's result if <expression> is an lvalue, or
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// not_an_lvalue() otherwise.
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struct not_an_lvalue {};
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template <class T>
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T& lvalue_preserver(T&, int);
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template <class U>
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not_an_lvalue lvalue_preserver(U const&, ...);
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# define BOOST_LVALUE_PRESERVER(expr) detail::lvalue_preserver(expr,0)
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#else
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# define BOOST_LVALUE_PRESERVER(expr) expr
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#endif
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// Guts of is_lvalue_iterator. Value is the iterator's value_type
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// and the result is computed in the nested rebind template.
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template <class Value>
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struct is_lvalue_iterator_impl
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{
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// Eat implicit conversions so we don't report true for things
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// convertible to Value const&
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struct conversion_eater
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{
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conversion_eater(Value&);
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};
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static char tester(conversion_eater, int);
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static char (& tester(any_conversion_eater, ...) )[2];
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template <class It>
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struct rebind
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{
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static It& x;
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BOOST_STATIC_CONSTANT(
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bool
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, value = (
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sizeof(
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is_lvalue_iterator_impl<Value>::tester(
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BOOST_LVALUE_PRESERVER(*x), 0
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)
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) == 1
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)
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);
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};
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};
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#undef BOOST_LVALUE_PRESERVER
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//
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// void specializations to handle std input and output iterators
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//
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template <>
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struct is_lvalue_iterator_impl<void>
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{
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template <class It>
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struct rebind : boost::mpl::false_
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{};
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};
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#ifndef BOOST_NO_CV_VOID_SPECIALIZATIONS
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template <>
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struct is_lvalue_iterator_impl<const void>
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{
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template <class It>
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struct rebind : boost::mpl::false_
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{};
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};
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template <>
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struct is_lvalue_iterator_impl<volatile void>
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{
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template <class It>
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struct rebind : boost::mpl::false_
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{};
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};
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template <>
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struct is_lvalue_iterator_impl<const volatile void>
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{
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template <class It>
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struct rebind : boost::mpl::false_
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{};
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};
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#endif
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//
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// This level of dispatching is required for Borland. We might save
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// an instantiation by removing it for others.
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//
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template <class It>
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struct is_readable_lvalue_iterator_impl
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: is_lvalue_iterator_impl<
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BOOST_DEDUCED_TYPENAME boost::detail::iterator_traits<It>::value_type const
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>::template rebind<It>
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{};
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template <class It>
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struct is_non_const_lvalue_iterator_impl
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: is_lvalue_iterator_impl<
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BOOST_DEDUCED_TYPENAME boost::detail::iterator_traits<It>::value_type
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>::template rebind<It>
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{};
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} // namespace detail
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// Define the trait with full mpl lambda capability and various broken
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// compiler workarounds
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BOOST_TT_AUX_BOOL_TRAIT_DEF1(
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is_lvalue_iterator,T,::boost::iterators::detail::is_readable_lvalue_iterator_impl<T>::value)
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BOOST_TT_AUX_BOOL_TRAIT_DEF1(
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is_non_const_lvalue_iterator,T,::boost::iterators::detail::is_non_const_lvalue_iterator_impl<T>::value)
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} // namespace iterators
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using iterators::is_lvalue_iterator;
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using iterators::is_non_const_lvalue_iterator;
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} // namespace boost
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#endif
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#include <boost/iterator/detail/config_undef.hpp>
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#include <boost/type_traits/detail/bool_trait_undef.hpp>
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#endif // IS_LVALUE_ITERATOR_DWA2003112_HPP
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