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/remove_cv.hpp>
13# include <boost/mpl/aux_/lambda_support.hpp>
14# include <boost/mpl/bool.hpp>
15# include <boost/detail/workaround.hpp>
16
17namespace boost { namespace iostreams { namespace detail {
18
19// is_dereferenceable<T> metafunction
20//
21// Requires: Given x of type T&, if the expression *x is well-formed
22// it must have complete type; otherwise, it must neither be ambiguous
23// nor violate access.
24
25// This namespace ensures that ADL doesn't mess things up.
26namespace is_dereferenceable_
27{
28 // a type returned from operator* when no increment is found in the
29 // type's own namespace
30 struct tag {};
31
32 // any soaks up implicit conversions and makes the following
33 // operator* less-preferred than any other such operator that
34 // might be found via ADL.
35 struct any { template <class T> any(T const&); };
36
37 // This is a last-resort operator* for when none other is found
38 tag operator*(any const&);
39
40# if BOOST_WORKAROUND(__MWERKS__, BOOST_TESTED_AT(0x3202))
41# define BOOST_comma(a,b) (a)
42# else
43 // In case an operator++ is found that returns void, we'll use ++x,0
44 tag operator,(tag,int);
45# define BOOST_comma(a,b) (a,b)
46# endif
47
48 // two check overloads help us identify which operator++ was picked
49 char (& check_increment(tag) )[2];
50
51 template <class T>
52 char check_increment(T const&);
53
54 template <class T>
55 struct impl
56 {
57 static typename boost::remove_cv<T>::type& x;
58
59 BOOST_STATIC_CONSTANT(
60 bool
61 , value = sizeof(is_dereferenceable_::check_increment(BOOST_comma(*x,0))) == 1
62 );
63 };
64}
65
66# undef BOOST_comma
67
68template<typename T>
69struct is_dereferenceable
70 : public ::boost::integral_constant<bool, is_dereferenceable_::impl<T>::value >
71{
72 BOOST_MPL_AUX_LAMBDA_SUPPORT(1,is_dereferenceable,(T))
73};
74
75} }
76
77
78} // End namespaces detail, iostreams, boost.
79
80#endif // BOOST_IOSTREAMS_DETAIL_IS_DEREFERENCEABLE_HPP_INCLUDED
81

source code of boost/libs/iostreams/include/boost/iostreams/detail/is_dereferenceable.hpp