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) 2016-2019 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>
23 #include <boost/type_traits/is_nothrow_move_constructible.hpp>
27 //////////////////////////////////////////////////////////////////////////
28 // class template recursive_wrapper
30 // Enables recursive types in templates by breaking cyclic dependencies.
36 // typedef variant< int, recursive_wrapper<my> > var;
43 template <typename T> class recursive_wrapper;
46 ///////////////////////////////////////////////////////////////////////////////
47 // metafunction is_constructible partial specializations.
49 // recursive_wrapper<T> is constructible only from T and recursive_wrapper<T>.
51 template <class T> struct is_constructible<recursive_wrapper<T>, T> : boost::true_type{};
52 template <class T> struct is_constructible<recursive_wrapper<T>, const T> : boost::true_type{};
53 template <class T> struct is_constructible<recursive_wrapper<T>, T&> : boost::true_type{};
54 template <class T> struct is_constructible<recursive_wrapper<T>, const T&> : boost::true_type{};
55 template <class T> struct is_constructible<recursive_wrapper<T>, recursive_wrapper<T> > : boost::true_type{};
56 template <class T> struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<T> > : boost::true_type{};
57 template <class T> struct is_constructible<recursive_wrapper<T>, recursive_wrapper<T>& > : boost::true_type{};
58 template <class T> struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<T>& > : boost::true_type{};
60 template <class T, class U> struct is_constructible<recursive_wrapper<T>, U > : boost::false_type{};
61 template <class T, class U> struct is_constructible<recursive_wrapper<T>, const U > : boost::false_type{};
62 template <class T, class U> struct is_constructible<recursive_wrapper<T>, U& > : boost::false_type{};
63 template <class T, class U> struct is_constructible<recursive_wrapper<T>, const U& > : boost::false_type{};
64 template <class T, class U> struct is_constructible<recursive_wrapper<T>, recursive_wrapper<U> > : boost::false_type{};
65 template <class T, class U> struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<U> > : boost::false_type{};
66 template <class T, class U> struct is_constructible<recursive_wrapper<T>, recursive_wrapper<U>& > : boost::false_type{};
67 template <class T, class U> struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<U>& > : boost::false_type{};
69 // recursive_wrapper is not nothrow move constructible, because it's constructor does dynamic memory allocation.
70 // This specialisation is required to workaround GCC6 issue: https://svn.boost.org/trac/boost/ticket/12680
71 template <class T> struct is_nothrow_move_constructible<recursive_wrapper<T> > : boost::false_type{};
73 ///////////////////////////////////////////////////////////////////////////////
74 // metafunction is_recursive_wrapper (modeled on code by David Abrahams)
76 // True if specified type matches recursive_wrapper<T>.
83 struct is_recursive_wrapper_impl
89 struct is_recursive_wrapper_impl< recursive_wrapper<T> >
97 template< typename T > struct is_recursive_wrapper
98 : public ::boost::integral_constant<bool,(::boost::detail::is_recursive_wrapper_impl<T>::value)>
101 BOOST_MPL_AUX_LAMBDA_SUPPORT(1,is_recursive_wrapper,(T))
104 ///////////////////////////////////////////////////////////////////////////////
105 // metafunction unwrap_recursive
107 // If specified type T matches recursive_wrapper<U>, then U; else T.
111 template <typename T>
112 struct unwrap_recursive
116 BOOST_MPL_AUX_LAMBDA_SUPPORT(1,unwrap_recursive,(T))
119 template <typename T>
120 struct unwrap_recursive< recursive_wrapper<T> >
124 BOOST_MPL_AUX_LAMBDA_SUPPORT_SPEC(1,unwrap_recursive,(T))
130 #endif // BOOST_VARIANT_RECURSIVE_WRAPPER_FWD_HPP