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1 | #ifndef BOOST_METAPARSE_V1_OPTIONAL_HPP |
2 | #define BOOST_METAPARSE_V1_OPTIONAL_HPP | |
3 | ||
4 | // Copyright Abel Sinkovics (abel@sinkovics.hu) 2015. | |
5 | // Distributed under the Boost Software License, Version 1.0. | |
6 | // (See accompanying file LICENSE_1_0.txt or copy at | |
7 | // http://www.boost.org/LICENSE_1_0.txt) | |
8 | ||
9 | #include <boost/metaparse/v1/is_error.hpp> | |
10 | #include <boost/metaparse/v1/accept.hpp> | |
11 | ||
12 | #include <boost/mpl/if.hpp> | |
13 | ||
14 | namespace boost | |
15 | { | |
16 | namespace metaparse | |
17 | { | |
18 | namespace v1 | |
19 | { | |
20 | template <class P, class Default = void> | |
21 | struct optional | |
22 | { | |
23 | typedef optional type; | |
24 | ||
25 | template <class S, class Pos> | |
26 | struct apply : | |
27 | boost::mpl::if_< | |
28 | is_error<typename P::template apply<S, Pos> >, | |
29 | accept<Default, S, Pos>, | |
30 | // is_error evaluates it anyway | |
31 | typename P::template apply<S, Pos>::type | |
32 | > | |
33 | {}; | |
34 | }; | |
35 | } | |
36 | } | |
37 | } | |
38 | ||
39 | #endif | |
40 |