ceph/src/boost/libs/hana/include/boost/hana/product.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::product`.
   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_PRODUCT_HPP
  11 #define BOOST_HANA_PRODUCT_HPP
  12
  13 #include <boost/hana/fwd/product.hpp>
  14
  15 #include <boost/hana/concept/foldable.hpp>
  16 #include <boost/hana/concept/ring.hpp>
  17 #include <boost/hana/config.hpp>
  18 #include <boost/hana/core/dispatch.hpp>
  19 #include <boost/hana/fold_left.hpp>
  20 #include <boost/hana/integral_constant.hpp> // required by fwd decl
  21 #include <boost/hana/mult.hpp>
  22 #include <boost/hana/one.hpp>
  23
  24
  25 BOOST_HANA_NAMESPACE_BEGIN
  26     template <typename R>
  27     struct product_t {
  28     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  29         static_assert(hana::Ring<R>::value,
  30         "hana::product<R> requires 'R' to be a Ring");
  31     #endif
  32
  33         template <typename Xs>
  34         constexpr decltype(auto) operator()(Xs&& xs) const {
  35             using S = typename hana::tag_of<Xs>::type;
  36             using Product = BOOST_HANA_DISPATCH_IF(product_impl<S>,
  37                 hana::Foldable<S>::value
  38             );
  39
  40         #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  41             static_assert(hana::Foldable<S>::value,
  42             "hana::product<R>(xs) requires 'xs' to be Foldable");
  43         #endif
  44
  45             return Product::template apply<R>(static_cast<Xs&&>(xs));
  46         }
  47     };
  48
  49     template <typename T, bool condition>
  50     struct product_impl<T, when<condition>> : default_ {
  51         template <typename R, typename Xs>
  52         static constexpr decltype(auto) apply(Xs&& xs) {
  53             return hana::fold_left(static_cast<Xs&&>(xs), hana::one<R>(), hana::mult);
  54         }
  55     };
  56 BOOST_HANA_NAMESPACE_END
  57
  58 #endif // !BOOST_HANA_PRODUCT_HPP