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92 lines
2.3 KiB
C++
92 lines
2.3 KiB
C++
// Copyright Daniel Wallin, David Abrahams 2005. Use, modification and
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// distribution is subject to 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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#ifndef UNWRAP_CV_REFERENCE_050328_HPP
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#define UNWRAP_CV_REFERENCE_050328_HPP
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#include <boost/parameter/aux_/yesno.hpp>
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#include <boost/mpl/bool.hpp>
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#include <boost/mpl/identity.hpp>
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#include <boost/mpl/eval_if.hpp>
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namespace boost { template<class T> class reference_wrapper; }
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namespace boost { namespace parameter { namespace aux {
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//
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// reference_wrapper support -- because of the forwarding problem,
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// when passing arguments positionally by non-const reference, we
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// ask users of named parameter interfaces to use ref(x) to wrap
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// them.
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//
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// is_cv_reference_wrapper returns mpl::true_ if T is of type
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// reference_wrapper<U> cv
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template <class U>
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yes_tag is_cv_reference_wrapper_check(reference_wrapper<U> const volatile*);
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no_tag is_cv_reference_wrapper_check(...);
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template <class T>
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struct is_cv_reference_wrapper
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{
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BOOST_STATIC_CONSTANT(
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bool, value = (
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sizeof(is_cv_reference_wrapper_check((T*)0)) == sizeof(yes_tag)
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)
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);
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typedef mpl::bool_<
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#if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
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is_cv_reference_wrapper::
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#endif
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value> type;
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};
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// Needed for unwrap_cv_reference below. T might be const, so
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// eval_if might fail because of deriving from T const on EDG.
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template <class T>
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struct get_type
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{
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typedef typename T::type type;
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};
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#if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
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template <class T, class is_reference_wrapper = typename is_cv_reference_wrapper<T>::type>
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struct unwrap_cv_reference
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{
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typedef T type;
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};
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template <class T>
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struct unwrap_cv_reference<T const, mpl::false_>
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{
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typedef T const type;
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};
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template <class T>
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struct unwrap_cv_reference<T, mpl::true_>
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: T
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{};
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#else
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// Produces the unwrapped type to hold a reference to in named<>
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// Can't use boost::unwrap_reference<> here because it
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// doesn't handle the case where T = reference_wrapper<U> cv
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template <class T>
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struct unwrap_cv_reference
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{
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typedef typename mpl::eval_if<
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is_cv_reference_wrapper<T>
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, get_type<T>
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, mpl::identity<T>
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>::type type;
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};
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#endif
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}}} // namespace boost::parameter::aux
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#endif // UNWRAP_CV_REFERENCE_050328_HPP
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