boost/hana/fill.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::fill`.
   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_FILL_HPP
  11 #define BOOST_HANA_FILL_HPP
  12
  13 #include <boost/hana/fwd/fill.hpp>
  14
  15 #include <boost/hana/concept/functor.hpp>
  16 #include <boost/hana/concept/sequence.hpp>
  17 #include <boost/hana/config.hpp>
  18 #include <boost/hana/core/dispatch.hpp>
  19 #include <boost/hana/core/make.hpp>
  20 #include <boost/hana/functional/always.hpp>
  21 #include <boost/hana/transform.hpp>
  22 #include <boost/hana/unpack.hpp>
  23
  24
  25 BOOST_HANA_NAMESPACE_BEGIN
  26     //! @cond
  27     template <typename Xs, typename Value>
  28     constexpr auto fill_t::operator()(Xs&& xs, Value&& value) const {
  29         using S = typename hana::tag_of<Xs>::type;
  30         using Fill = BOOST_HANA_DISPATCH_IF(fill_impl<S>,
  31             hana::Functor<S>::value
  32         );
  33
  34     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  35         static_assert(hana::Functor<S>::value,
  36         "hana::fill(xs, value) requires 'xs' to be a Functor");
  37     #endif
  38
  39         return Fill::apply(static_cast<Xs&&>(xs),
  40                            static_cast<Value&&>(value));
  41     }
  42     //! @endcond
  43
  44     template <typename Fun, bool condition>
  45     struct fill_impl<Fun, when<condition>> : default_ {
  46         template <typename Xs, typename Value>
  47         static constexpr auto apply(Xs&& xs, Value&& v) {
  48             return hana::transform(static_cast<Xs&&>(xs),
  49                                    hana::always(static_cast<Value&&>(v))
  50             );
  51         }
  52     };
  53
  54     template <typename S>
  55     struct fill_impl<S, when<Sequence<S>::value>> {
  56         //! @cond
  57         template <typename V>
  58         struct filler {
  59             V const& v;
  60             template <typename ...Xs>
  61             constexpr auto operator()(Xs const& ...xs) const {
  62                 return hana::make<S>(((void)xs, v)...);
  63             }
  64         };
  65         //! @endcond
  66
  67         template <typename Xs, typename V>
  68         static constexpr auto apply(Xs const& xs, V const& v) {
  69             return hana::unpack(xs, filler<V>{v});
  70         }
  71     };
  72 BOOST_HANA_NAMESPACE_END
  73
  74 #endif // !BOOST_HANA_FILL_HPP