boost/hana/count.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::count`.
   4
   5 @copyright Louis Dionne 2013-2017
   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_COUNT_HPP
  11 #define BOOST_HANA_COUNT_HPP
  12
  13 #include <boost/hana/fwd/count.hpp>
  14
  15 #include <boost/hana/concept/foldable.hpp>
  16 #include <boost/hana/config.hpp>
  17 #include <boost/hana/core/dispatch.hpp>
  18 #include <boost/hana/count_if.hpp>
  19 #include <boost/hana/equal.hpp>
  20
  21
  22 BOOST_HANA_NAMESPACE_BEGIN
  23     //! @cond
  24     template <typename Xs, typename Value>
  25     constexpr auto count_t::operator()(Xs&& xs, Value&& value) const {
  26         using S = typename hana::tag_of<Xs>::type;
  27         using Count = BOOST_HANA_DISPATCH_IF(count_impl<S>,
  28             hana::Foldable<S>::value
  29         );
  30
  31     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  32         static_assert(hana::Foldable<S>::value,
  33         "hana::count(xs, value) requires 'xs' to be Foldable");
  34     #endif
  35
  36         return Count::apply(static_cast<Xs&&>(xs), static_cast<Value&&>(value));
  37     }
  38     //! @endcond
  39
  40     template <typename T, bool condition>
  41     struct count_impl<T, when<condition>> : default_ {
  42         template <typename Xs, typename Value>
  43         static constexpr auto apply(Xs&& xs, Value&& value) {
  44             return hana::count_if(static_cast<Xs&&>(xs),
  45                 hana::equal.to(static_cast<Value&&>(value)));
  46         }
  47     };
  48 BOOST_HANA_NAMESPACE_END
  49
  50 #endif // !BOOST_HANA_COUNT_HPP