81 lines
2.4 KiB
C++
81 lines
2.4 KiB
C++
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// (C) Copyright 2008 CodeRage, LLC (turkanis at coderage dot com)
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// (C) Copyright 2005-2007 Jonathan Turkanis
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// (C) Copyright David Abrahams 2004.
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// Distributed under 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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// See http://www.boost.org/libs/iostreams for documentation.
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#ifndef BOOST_IOSTREAMS_DETAIL_IS_DEREFERENCEABLE_HPP_INCLUDED
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#define BOOST_IOSTREAMS_DETAIL_IS_DEREFERENCEABLE_HPP_INCLUDED
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# include <boost/type_traits/remove_cv.hpp>
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# include <boost/mpl/aux_/lambda_support.hpp>
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# include <boost/mpl/bool.hpp>
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# include <boost/detail/workaround.hpp>
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namespace boost { namespace iostreams { namespace detail {
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// is_dereferenceable<T> metafunction
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//
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// Requires: Given x of type T&, if the expression *x is well-formed
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// it must have complete type; otherwise, it must neither be ambiguous
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// nor violate access.
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// This namespace ensures that ADL doesn't mess things up.
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namespace is_dereferenceable_
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{
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// a type returned from operator* when no increment is found in the
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// type's own namespace
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struct tag {};
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// any soaks up implicit conversions and makes the following
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// operator* less-preferred than any other such operator that
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// might be found via ADL.
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struct any { template <class T> any(T const&); };
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// This is a last-resort operator* for when none other is found
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tag operator*(any const&);
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# if BOOST_WORKAROUND(__MWERKS__, BOOST_TESTED_AT(0x3202))
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# define BOOST_comma(a,b) (a)
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# else
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// In case an operator++ is found that returns void, we'll use ++x,0
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tag operator,(tag,int);
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# define BOOST_comma(a,b) (a,b)
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# endif
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// two check overloads help us identify which operator++ was picked
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char (& check_increment(tag) )[2];
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template <class T>
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char check_increment(T const&);
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template <class T>
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struct impl
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{
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static typename boost::remove_cv<T>::type& x;
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BOOST_STATIC_CONSTANT(
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bool
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, value = sizeof(is_dereferenceable_::check_increment(BOOST_comma(*x,0))) == 1
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);
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};
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}
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# undef BOOST_comma
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template<typename T>
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struct is_dereferenceable
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: public ::boost::integral_constant<bool, is_dereferenceable_::impl<T>::value >
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{
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BOOST_MPL_AUX_LAMBDA_SUPPORT(1,is_dereferenceable,(T))
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};
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} }
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} // End namespaces detail, iostreams, boost.
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#endif // BOOST_IOSTREAMS_DETAIL_IS_DEREFERENCEABLE_HPP_INCLUDED
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