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

   1 /*!
   2 @file
   3 Forward declares `boost::hana::find`.
   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_FIND_HPP
  11 #define BOOST_HANA_FWD_FIND_HPP
  12
  13 #include <boost/hana/config.hpp>
  14 #include <boost/hana/core/when.hpp>
  15
  16
  17 BOOST_HANA_NAMESPACE_BEGIN
  18     //! Finds the value associated to the given key in a structure.
  19     //! @ingroup group-Searchable
  20     //!
  21     //! Given a `key` and a `Searchable` structure, `find` returns the `just`
  22     //! the first value whose key is equal to the given `key`, or `nothing` if
  23     //! there is no such key. Comparison is done with `equal`. `find` satisfies
  24     //! the following:
  25     //! @code
  26     //!     find(xs, key) == find_if(xs, equal.to(key))
  27     //! @endcode
  28     //!
  29     //!
  30     //! @param xs
  31     //! The structure to be searched.
  32     //!
  33     //! @param key
  34     //! A key to be searched for in the structure. The key has to be
  35     //! `Comparable` with the other keys of the structure. In the current
  36     //! version of the library, the comparison of `key` with any other key
  37     //! of the structure must return a compile-time `Logical`.
  38     //!
  39     //!
  40     //! Example
  41     //! -------
  42     //! @include example/find.cpp
  43 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  44     constexpr auto find = [](auto&& xs, auto const& key) {
  45         return tag-dispatched;
  46     };
  47 #else
  48     template <typename S, typename = void>
  49     struct find_impl : find_impl<S, when<true>> { };
  50
  51     struct find_t {
  52         template <typename Xs, typename Key>
  53         constexpr auto operator()(Xs&& xs, Key const& key) const;
  54     };
  55
  56     constexpr find_t find{};
  57 #endif
  58 BOOST_HANA_NAMESPACE_END
  59
  60 #endif // !BOOST_HANA_FWD_FIND_HPP