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85 lines
2.7 KiB
85 lines
2.7 KiB
// (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/detail/bool_trait_def.hpp> |
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# include <boost/type_traits/detail/template_arity_spec.hpp> |
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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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|| BOOST_WORKAROUND(BOOST_MSVC, <= 1300) |
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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 BOOST_PREVENT_MACRO_SUBSTITUTION(tag) )[2]; |
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template <class T> |
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char check BOOST_PREVENT_MACRO_SUBSTITUTION(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 BOOST_PREVENT_MACRO_SUBSTITUTION(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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BOOST_TT_AUX_BOOL_C_BASE(is_dereferenceable_::impl<T>::value) |
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{ |
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BOOST_TT_AUX_BOOL_TRAIT_VALUE_DECL(is_dereferenceable_::impl<T>::value) |
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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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BOOST_TT_AUX_TEMPLATE_ARITY_SPEC(1, ::boost::iostreams::detail::is_dereferenceable) |
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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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