transducer_impl.hpp

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//
// Copyright (C) 2014, 2015 Ableton AG, Berlin. All rights reserved.
//
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#pragma once

#include <atria/estd/type_traits.hpp>
#include <atria/estd/utility.hpp>
#include <tuple>

namespace atria {
namespace xform {

template<typename ReducingFnGenT,
         typename ...ParamTs>
struct transducer_impl : std::tuple<ParamTs...>
{
  using base_t = std::tuple<ParamTs...>;

  // Constructors need to be semi-manually defined.  Otherwise
  // confusion arises because of the way Clang's std::tuple uses
  // enable_if to dispatch to the right move constructors.
  //
  //    using base_t::base_t;

  transducer_impl() = default;
  transducer_impl(const transducer_impl&) = default;
  transducer_impl(transducer_impl&&) = default;
  transducer_impl& operator=(const transducer_impl&) = default;
  transducer_impl& operator=(transducer_impl&&) = default;

  template <typename ...Ts>
  transducer_impl(Ts ...ts)
    : base_t(std::move(ts)...)
  {}

  template<typename ReducingFnT>
  constexpr auto operator() (ReducingFnT&& step) const
    -> typename ReducingFnGenT::template apply<
      estd::decay_t<ReducingFnT>,
      estd::decay_t<ParamTs>...
    >
  {
    using indexes_t = estd::make_index_sequence<sizeof...(ParamTs)>;
    return this->make(std::forward<ReducingFnT>(step), indexes_t());
  }

  template<typename ReducingFnT, std::size_t...indexes_t>
  constexpr auto make(ReducingFnT&& step, estd::index_sequence<indexes_t...>) const
    -> typename ReducingFnGenT::template apply<
      estd::decay_t<ReducingFnT>,
      estd::decay_t<ParamTs>...
    >
  {
    return { std::forward<ReducingFnT>(step),
             std::get<indexes_t>(*this)... };
  }
};

} // namespace xform
} // namespace atria