1//-----------------------------------------------------------------------------
2// boost variant/recursive_wrapper_fwd.hpp header file
3// See http://www.boost.org for updates, documentation, and revision history.
4//-----------------------------------------------------------------------------
5//
6// Copyright (c) 2002 Eric Friedman, Itay Maman
7// Copyright (c) 2016-2023 Antony Polukhin
8//
9// Portions Copyright (C) 2002 David Abrahams
10//
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)
14
15#ifndef BOOST_VARIANT_RECURSIVE_WRAPPER_FWD_HPP
16#define BOOST_VARIANT_RECURSIVE_WRAPPER_FWD_HPP
17
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>
24
25namespace boost {
26
27//////////////////////////////////////////////////////////////////////////
28// class template recursive_wrapper
29//
30// Enables recursive types in templates by breaking cyclic dependencies.
31//
32// For example:
33//
34// class my;
35//
36// typedef variant< int, recursive_wrapper<my> > var;
37//
38// class my {
39// var var_;
40// ...
41// };
42//
43template <typename T> class recursive_wrapper;
44
45
46///////////////////////////////////////////////////////////////////////////////
47// metafunction is_constructible partial specializations.
48//
49// recursive_wrapper<T> is constructible only from T and recursive_wrapper<T>.
50//
51template <class T> struct is_constructible<recursive_wrapper<T>, T> : boost::true_type{};
52template <class T> struct is_constructible<recursive_wrapper<T>, const T> : boost::true_type{};
53template <class T> struct is_constructible<recursive_wrapper<T>, T&> : boost::true_type{};
54template <class T> struct is_constructible<recursive_wrapper<T>, const T&> : boost::true_type{};
55template <class T> struct is_constructible<recursive_wrapper<T>, recursive_wrapper<T> > : boost::true_type{};
56template <class T> struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<T> > : boost::true_type{};
57template <class T> struct is_constructible<recursive_wrapper<T>, recursive_wrapper<T>& > : boost::true_type{};
58template <class T> struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<T>& > : boost::true_type{};
59
60template <class T, class U> struct is_constructible<recursive_wrapper<T>, U > : boost::false_type{};
61template <class T, class U> struct is_constructible<recursive_wrapper<T>, const U > : boost::false_type{};
62template <class T, class U> struct is_constructible<recursive_wrapper<T>, U& > : boost::false_type{};
63template <class T, class U> struct is_constructible<recursive_wrapper<T>, const U& > : boost::false_type{};
64template <class T, class U> struct is_constructible<recursive_wrapper<T>, recursive_wrapper<U> > : boost::false_type{};
65template <class T, class U> struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<U> > : boost::false_type{};
66template <class T, class U> struct is_constructible<recursive_wrapper<T>, recursive_wrapper<U>& > : boost::false_type{};
67template <class T, class U> struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<U>& > : boost::false_type{};
68
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
71template <class T> struct is_nothrow_move_constructible<recursive_wrapper<T> > : boost::false_type{};
72
73///////////////////////////////////////////////////////////////////////////////
74// metafunction is_recursive_wrapper (modeled on code by David Abrahams)
75//
76// True if specified type matches recursive_wrapper<T>.
77//
78
79namespace detail {
80
81
82template <typename T>
83struct is_recursive_wrapper_impl
84 : mpl::false_
85{
86};
87
88template <typename T>
89struct is_recursive_wrapper_impl< recursive_wrapper<T> >
90 : mpl::true_
91{
92};
93
94
95} // namespace detail
96
97template< typename T > struct is_recursive_wrapper
98 : public ::boost::integral_constant<bool,(::boost::detail::is_recursive_wrapper_impl<T>::value)>
99{
100public:
101 BOOST_MPL_AUX_LAMBDA_SUPPORT(1,is_recursive_wrapper,(T))
102};
103
104///////////////////////////////////////////////////////////////////////////////
105// metafunction unwrap_recursive
106//
107// If specified type T matches recursive_wrapper<U>, then U; else T.
108//
109
110
111template <typename T>
112struct unwrap_recursive
113{
114 typedef T type;
115
116 BOOST_MPL_AUX_LAMBDA_SUPPORT(1,unwrap_recursive,(T))
117};
118
119template <typename T>
120struct unwrap_recursive< recursive_wrapper<T> >
121{
122 typedef T type;
123
124 BOOST_MPL_AUX_LAMBDA_SUPPORT_SPEC(1,unwrap_recursive,(T))
125};
126
127
128} // namespace boost
129
130#endif // BOOST_VARIANT_RECURSIVE_WRAPPER_FWD_HPP
131