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 17 namespace 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. 26 namespace 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 68 template<typename T> 69 struct 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