ceph/src/boost/libs/hana/include/boost/hana/fwd/is_subset.hpp

   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