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1 | /*! |
2 | @file | |
3 | Forward declares `boost::hana::is_subset`. | |
4 | ||
5 | @copyright Louis Dionne 2013-2016 | |
6 | Distributed under the Boost Software License, Version 1.0. | |
7 | (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) | |
8 | */ | |
9 | ||
10 | #ifndef BOOST_HANA_FWD_IS_SUBSET_HPP | |
11 | #define BOOST_HANA_FWD_IS_SUBSET_HPP | |
12 | ||
13 | #include <boost/hana/config.hpp> | |
14 | #include <boost/hana/core/when.hpp> | |
15 | ||
16 | #include <boost/hana/functional/infix.hpp> | |
17 | ||
18 | ||
19 | BOOST_HANA_NAMESPACE_BEGIN | |
20 | //! Returns whether a structure contains a subset of the keys of | |
21 | //! another structure. | |
22 | //! @ingroup group-Searchable | |
23 | //! | |
24 | //! Given two `Searchable`s `xs` and `ys`, `is_subset` returns a `Logical` | |
25 | //! representing whether `xs` is a subset of `ys`. In other words, it | |
26 | //! returns whether all the keys of `xs` are also present in `ys`. This | |
27 | //! method does not return whether `xs` is a _strict_ subset of `ys`; if | |
28 | //! `xs` and `ys` are equal, all the keys of `xs` are also present in | |
29 | //! `ys`, and `is_subset` returns true. | |
30 | //! | |
31 | //! @note | |
32 | //! For convenience, `is_subset` can also be applied in infix notation. | |
33 | //! | |
34 | //! | |
35 | //! Cross-type version of the method | |
36 | //! -------------------------------- | |
37 | //! This method is tag-dispatched using the tags of both arguments. | |
38 | //! It can be called with any two `Searchable`s sharing a common | |
39 | //! `Searchable` embedding, as defined in the main documentation | |
40 | //! of the `Searchable` concept. When `Searchable`s with two different | |
41 | //! tags but sharing a common embedding are sent to `is_subset`, they | |
42 | //! are first converted to this common `Searchable` and the `is_subset` | |
43 | //! method of the common embedding is then used. Of course, the method | |
44 | //! can be overriden for custom `Searchable`s for efficieny. | |
45 | //! | |
46 | //! @note | |
47 | //! While cross-type dispatching for `is_subset` is supported, it is | |
48 | //! not currently used by the library because there are no models | |
49 | //! of `Searchable` with a common embedding. | |
50 | //! | |
51 | //! | |
52 | //! @param xs | |
53 | //! The structure to check whether it is a subset of `ys`. | |
54 | //! | |
55 | //! @param ys | |
56 | //! The structure to check whether it is a superset of `xs`. | |
57 | //! | |
58 | //! | |
59 | //! Example | |
60 | //! ------- | |
61 | //! @include example/is_subset.cpp | |
62 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
63 | constexpr auto is_subset = [](auto&& xs, auto&& ys) { | |
64 | return tag-dispatched; | |
65 | }; | |
66 | #else | |
67 | template <typename S1, typename S2, typename = void> | |
68 | struct is_subset_impl : is_subset_impl<S1, S2, when<true>> { }; | |
69 | ||
70 | struct is_subset_t { | |
71 | template <typename Xs, typename Ys> | |
72 | constexpr auto operator()(Xs&& xs, Ys&& ys) const; | |
73 | }; | |
74 | ||
75 | constexpr auto is_subset = hana::infix(is_subset_t{}); | |
76 | #endif | |
77 | BOOST_HANA_NAMESPACE_END | |
78 | ||
79 | #endif // !BOOST_HANA_FWD_IS_SUBSET_HPP |