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/Src/Dependencies/Boost/boost/iostreams/detail/is_dereferenceable.hpp

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 1// (C) Copyright 2008 CodeRage, LLC (turkanis at coderage dot com)
 2// (C) Copyright 2005-2007 Jonathan Turkanis
 3// (C) Copyright David Abrahams 2004.
 4// Distributed under the Boost Software License, Version 1.0. (See accompanying
 5// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt.)
 6
 7// See http://www.boost.org/libs/iostreams for documentation.
 8
 9#ifndef BOOST_IOSTREAMS_DETAIL_IS_DEREFERENCEABLE_HPP_INCLUDED
10#define BOOST_IOSTREAMS_DETAIL_IS_DEREFERENCEABLE_HPP_INCLUDED
11
12# include <boost/type_traits/detail/bool_trait_def.hpp>
13# include <boost/type_traits/detail/template_arity_spec.hpp>
14# include <boost/type_traits/remove_cv.hpp>
15# include <boost/mpl/aux_/lambda_support.hpp>
16# include <boost/mpl/bool.hpp>
17# include <boost/detail/workaround.hpp>
18
19namespace boost { namespace iostreams { namespace detail { 
20
21// is_dereferenceable<T> metafunction
22//
23// Requires: Given x of type T&, if the expression *x is well-formed
24// it must have complete type; otherwise, it must neither be ambiguous
25// nor violate access.
26
27// This namespace ensures that ADL doesn't mess things up.
28namespace is_dereferenceable_
29{
30  // a type returned from operator* when no increment is found in the
31  // type's own namespace
32  struct tag {};
33  
34  // any soaks up implicit conversions and makes the following
35  // operator* less-preferred than any other such operator that
36  // might be found via ADL.
37  struct any { template <class T> any(T const&); };
38
39  // This is a last-resort operator* for when none other is found
40  tag operator*(any const&);
41
42# if BOOST_WORKAROUND(__MWERKS__, BOOST_TESTED_AT(0x3202)) \
43    || BOOST_WORKAROUND(BOOST_MSVC, <= 1300)
44#  define BOOST_comma(a,b) (a)
45# else 
46  // In case an operator++ is found that returns void, we'll use ++x,0
47  tag operator,(tag,int);  
48#  define BOOST_comma(a,b) (a,b)
49# endif 
50  
51  // two check overloads help us identify which operator++ was picked
52  char (& check BOOST_PREVENT_MACRO_SUBSTITUTION(tag) )[2];
53  
54  template <class T>
55  char check BOOST_PREVENT_MACRO_SUBSTITUTION(T const&);
56  
57  template <class T>
58  struct impl
59  {
60      static typename boost::remove_cv<T>::type& x;
61
62      BOOST_STATIC_CONSTANT(
63          bool
64        , value = sizeof(is_dereferenceable_::check BOOST_PREVENT_MACRO_SUBSTITUTION(BOOST_comma(*x,0))) == 1
65      );
66  };
67}
68
69# undef BOOST_comma
70
71template<typename T> 
72struct is_dereferenceable 
73    BOOST_TT_AUX_BOOL_C_BASE(is_dereferenceable_::impl<T>::value)
74{ 
75    BOOST_TT_AUX_BOOL_TRAIT_VALUE_DECL(is_dereferenceable_::impl<T>::value)
76    BOOST_MPL_AUX_LAMBDA_SUPPORT(1,is_dereferenceable,(T))
77};
78
79} } 
80
81BOOST_TT_AUX_TEMPLATE_ARITY_SPEC(1, ::boost::iostreams::detail::is_dereferenceable)
82
83} // End namespaces detail, iostreams, boost.
84
85#endif // BOOST_IOSTREAMS_DETAIL_IS_DEREFERENCEABLE_HPP_INCLUDED