1 //-----------------------------------------------------------------------------
2 // boost variant/recursive_wrapper_fwd.hpp header file
3 // See http://www.boost.org for updates, documentation, and revision history.
4 //-----------------------------------------------------------------------------
6 // Copyright (c) 2002 Eric Friedman, Itay Maman
7 // Copyright (c) 2016 Antony Polukhin
9 // Portions Copyright (C) 2002 David Abrahams
11 // Distributed under the Boost Software License, Version 1.0. (See
12 // accompanying file LICENSE_1_0.txt or copy at
13 // http://www.boost.org/LICENSE_1_0.txt)
15 #ifndef BOOST_VARIANT_RECURSIVE_WRAPPER_FWD_HPP
16 #define BOOST_VARIANT_RECURSIVE_WRAPPER_FWD_HPP
18 #include <boost/mpl/bool.hpp>
19 #include <boost/mpl/aux_/config/ctps.hpp>
20 #include <boost/mpl/aux_/lambda_support.hpp>
21 #include <boost/type_traits/integral_constant.hpp>
22 #include <boost/type_traits/is_constructible.hpp>
26 //////////////////////////////////////////////////////////////////////////
27 // class template recursive_wrapper
29 // Enables recursive types in templates by breaking cyclic dependencies.
35 // typedef variant< int, recursive_wrapper<my> > var;
42 template <typename T> class recursive_wrapper;
45 ///////////////////////////////////////////////////////////////////////////////
46 // metafunction is_constructible partial specializations.
48 // recursive_wrapper<T> is constructible only from T and recursive_wrapper<T>.
50 template <class T> struct is_constructible<recursive_wrapper<T>, T> : boost::true_type{};
51 template <class T> struct is_constructible<recursive_wrapper<T>, const T> : boost::true_type{};
52 template <class T> struct is_constructible<recursive_wrapper<T>, T&> : boost::true_type{};
53 template <class T> struct is_constructible<recursive_wrapper<T>, const T&> : boost::true_type{};
54 template <class T> struct is_constructible<recursive_wrapper<T>, recursive_wrapper<T> > : boost::true_type{};
55 template <class T> struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<T> > : boost::true_type{};
56 template <class T> struct is_constructible<recursive_wrapper<T>, recursive_wrapper<T>& > : boost::true_type{};
57 template <class T> struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<T>& > : boost::true_type{};
59 template <class T, class U> struct is_constructible<recursive_wrapper<T>, U > : boost::false_type{};
60 template <class T, class U> struct is_constructible<recursive_wrapper<T>, const U > : boost::false_type{};
61 template <class T, class U> struct is_constructible<recursive_wrapper<T>, U& > : boost::false_type{};
62 template <class T, class U> struct is_constructible<recursive_wrapper<T>, const U& > : boost::false_type{};
63 template <class T, class U> struct is_constructible<recursive_wrapper<T>, recursive_wrapper<U> > : boost::false_type{};
64 template <class T, class U> struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<U> > : boost::false_type{};
65 template <class T, class U> struct is_constructible<recursive_wrapper<T>, recursive_wrapper<U>& > : boost::false_type{};
66 template <class T, class U> struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<U>& > : boost::false_type{};
69 ///////////////////////////////////////////////////////////////////////////////
70 // metafunction is_recursive_wrapper (modeled on code by David Abrahams)
72 // True if specified type matches recursive_wrapper<T>.
79 struct is_recursive_wrapper_impl
85 struct is_recursive_wrapper_impl< recursive_wrapper<T> >
93 template< typename T > struct is_recursive_wrapper
94 : public ::boost::integral_constant<bool,(::boost::detail::is_recursive_wrapper_impl<T>::value)>
97 BOOST_MPL_AUX_LAMBDA_SUPPORT(1,is_recursive_wrapper,(T))
100 ///////////////////////////////////////////////////////////////////////////////
101 // metafunction unwrap_recursive
103 // If specified type T matches recursive_wrapper<U>, then U; else T.
107 template <typename T>
108 struct unwrap_recursive
112 BOOST_MPL_AUX_LAMBDA_SUPPORT(1,unwrap_recursive,(T))
115 template <typename T>
116 struct unwrap_recursive< recursive_wrapper<T> >
120 BOOST_MPL_AUX_LAMBDA_SUPPORT_SPEC(1,unwrap_recursive,(T))
126 #endif // BOOST_VARIANT_RECURSIVE_WRAPPER_FWD_HPP