// (C) Copyright 2008 CodeRage, LLC (turkanis at coderage dot com) | |
// (C) Copyright 2005-2007 Jonathan Turkanis | |
// (C) Copyright David Abrahams 2004. | |
// Distributed under the Boost Software License, Version 1.0. (See accompanying | |
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt.) | |
// See http://www.boost.org/libs/iostreams for documentation. | |
#ifndef BOOST_IOSTREAMS_DETAIL_IS_DEREFERENCEABLE_HPP_INCLUDED | |
#define BOOST_IOSTREAMS_DETAIL_IS_DEREFERENCEABLE_HPP_INCLUDED | |
# include <boost/type_traits/detail/bool_trait_def.hpp> | |
# include <boost/type_traits/detail/template_arity_spec.hpp> | |
# include <boost/type_traits/remove_cv.hpp> | |
# include <boost/mpl/aux_/lambda_support.hpp> | |
# include <boost/mpl/bool.hpp> | |
# include <boost/detail/workaround.hpp> | |
namespace boost { namespace iostreams { namespace detail { | |
// is_dereferenceable<T> metafunction | |
// | |
// Requires: Given x of type T&, if the expression *x is well-formed | |
// it must have complete type; otherwise, it must neither be ambiguous | |
// nor violate access. | |
// This namespace ensures that ADL doesn't mess things up. | |
namespace is_dereferenceable_ | |
{ | |
// a type returned from operator* when no increment is found in the | |
// type's own namespace | |
struct tag {}; | |
// any soaks up implicit conversions and makes the following | |
// operator* less-preferred than any other such operator that | |
// might be found via ADL. | |
struct any { template <class T> any(T const&); }; | |
// This is a last-resort operator* for when none other is found | |
tag operator*(any const&); | |
# if BOOST_WORKAROUND(__MWERKS__, BOOST_TESTED_AT(0x3202)) \ | |
|| BOOST_WORKAROUND(BOOST_MSVC, <= 1300) | |
# define BOOST_comma(a,b) (a) | |
# else | |
// In case an operator++ is found that returns void, we'll use ++x,0 | |
tag operator,(tag,int); | |
# define BOOST_comma(a,b) (a,b) | |
# endif | |
// two check overloads help us identify which operator++ was picked | |
char (& check BOOST_PREVENT_MACRO_SUBSTITUTION(tag) )[2]; | |
template <class T> | |
char check BOOST_PREVENT_MACRO_SUBSTITUTION(T const&); | |
template <class T> | |
struct impl | |
{ | |
static typename boost::remove_cv<T>::type& x; | |
BOOST_STATIC_CONSTANT( | |
bool | |
, value = sizeof(is_dereferenceable_::check BOOST_PREVENT_MACRO_SUBSTITUTION(BOOST_comma(*x,0))) == 1 | |
); | |
}; | |
} | |
# undef BOOST_comma | |
template<typename T> | |
struct is_dereferenceable | |
BOOST_TT_AUX_BOOL_C_BASE(is_dereferenceable_::impl<T>::value) | |
{ | |
BOOST_TT_AUX_BOOL_TRAIT_VALUE_DECL(is_dereferenceable_::impl<T>::value) | |
BOOST_MPL_AUX_LAMBDA_SUPPORT(1,is_dereferenceable,(T)) | |
}; | |
} } | |
BOOST_TT_AUX_TEMPLATE_ARITY_SPEC(1, ::boost::iostreams::detail::is_dereferenceable) | |
} // End namespaces detail, iostreams, boost. | |
#endif // BOOST_IOSTREAMS_DETAIL_IS_DEREFERENCEABLE_HPP_INCLUDED |