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1 | /*============================================================================= |
2 | Copyright (c) 2001-2014 Joel de Guzman | |
3 | http://spirit.sourceforge.net/ | |
4 | ||
5 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
6 | file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) | |
7 | =============================================================================*/ | |
8 | #if !defined(BOOST_SPIRIT_X3_VARIANT_HAS_SUBSTITUTE_APR_18_2014_925AM) | |
9 | #define BOOST_SPIRIT_X3_VARIANT_HAS_SUBSTITUTE_APR_18_2014_925AM | |
10 | ||
11 | #include <boost/spirit/home/x3/support/traits/is_substitute.hpp> | |
12 | ||
13 | namespace boost { namespace spirit { namespace x3 { namespace traits | |
14 | { | |
15 | template <typename Variant, typename Attribute> | |
16 | struct variant_has_substitute_impl | |
17 | { | |
18 | // Find a type from the variant that can be a substitute for Attribute. | |
19 | // return true_ if one is found, else false_ | |
20 | ||
21 | typedef Variant variant_type; | |
22 | typedef typename variant_type::types types; | |
23 | typedef typename mpl::end<types>::type end; | |
24 | ||
25 | typedef typename | |
26 | mpl::find_if<types, is_same<mpl::_1, Attribute>>::type | |
27 | iter_1; | |
28 | ||
29 | typedef typename | |
30 | mpl::eval_if< | |
31 | is_same<iter_1, end>, | |
32 | mpl::find_if<types, traits::is_substitute<mpl::_1, Attribute>>, | |
33 | mpl::identity<iter_1> | |
34 | >::type | |
35 | iter; | |
36 | ||
37 | typedef mpl::not_<is_same<iter, end>> type; | |
38 | }; | |
39 | ||
40 | template <typename Variant, typename Attribute> | |
41 | struct variant_has_substitute | |
42 | : variant_has_substitute_impl<Variant, Attribute>::type {}; | |
43 | ||
44 | template <typename Attribute> | |
45 | struct variant_has_substitute<unused_type, Attribute> : mpl::true_ {}; | |
46 | ||
47 | template <typename Attribute> | |
48 | struct variant_has_substitute<unused_type const, Attribute> : mpl::true_ {}; | |
49 | ||
50 | }}}} | |
51 | ||
52 | #endif |