ceph/src/boost/boost/hana/fwd/index_if.hpp

   1 /*!
   2 @file
   3 Forward declares `boost::hana::index_if`.
   4
   5 @copyright Louis Dionne 2013-2017
   6 @copyright Jason Rice 2017
   7 Distributed under the Boost Software License, Version 1.0.
   8 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
   9  */
  10
  11 #ifndef BOOST_HANA_FWD_INDEX_IF_HPP
  12 #define BOOST_HANA_FWD_INDEX_IF_HPP
  13
  14 #include <boost/hana/config.hpp>
  15 #include <boost/hana/core/when.hpp>
  16
  17
  18 BOOST_HANA_NAMESPACE_BEGIN
  19     //! Finds the value associated to the first key satisfying a predicate.
  20     //! @ingroup group-Iterable
  21     //!
  22     //! Given an `Iterable` structure `xs` and a predicate `pred`,
  23     //! `index_if(xs, pred)` returns a `hana::optional` containing an `IntegralConstant`
  24     //! of the index of the first element that satisfies the predicate or nothing
  25     //! if no element satisfies the predicate.
  26     //!
  27     //!
  28     //! @param xs
  29     //! The structure to be searched.
  30     //!
  31     //! @param predicate
  32     //! A function called as `predicate(x)`, where `x` is an element of the
  33     //! `Iterable` structure and returning whether `x` is the element being
  34     //! searched for. In the current version of the library, the predicate
  35     //! has to return an `IntegralConstant` holding a value that can be
  36     //! converted to `bool`.
  37     //!
  38     //!
  39     //! Example
  40     //! -------
  41     //! @include example/index_if.cpp
  42 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  43     constexpr auto index_if = [](auto&& xs, auto&& predicate) {
  44         return tag-dispatched;
  45     };
  46 #else
  47     template <typename S, typename = void>
  48     struct index_if_impl : index_if_impl<S, when<true>> { };
  49
  50     struct index_if_t {
  51         template <typename Xs, typename Pred>
  52         constexpr auto operator()(Xs&& xs, Pred&& pred) const;
  53     };
  54
  55     constexpr index_if_t index_if{};
  56 #endif
  57 BOOST_HANA_NAMESPACE_END
  58
  59 #endif // !BOOST_HANA_FWD_INDEX_IF_HPP
  60