enumerate.hpp

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//
// Copyright (C) 2014, 2015 Ableton AG, Berlin. All rights reserved.
//
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// copy of this software and associated documentation files (the "Software"),
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// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
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#pragma once

#include <atria/xform/transducer_impl.hpp>
#include <atria/xform/state_wrapper.hpp>
#include <atria/prelude/constantly.hpp>
#include <atria/meta/utils.hpp>

namespace atria {
namespace xform {

#if ABL_CXX14

auto enumerate_from = [](auto initial) mutable
{
  return [=](auto step) mutable
  {
    return [=](auto&& s, auto&& ...is) mutable
    {
      auto count = state_data(ABL_FORWARD(s), constantly(initial));
      return wrap_state(
        step(state_unwrap(ABL_FORWARD(s)),
             std::move(count),
             ABL_FORWARD(is)...),
        decltype(initial)(std::move(count) + 1));
    };
  };
};

auto enumerate = enumerate_from(std::size_t{});

#else // ABL_CXX14

namespace detail {

struct enumerate_rf_gen
{
  template <typename ReducingFnT,
            typename IntegralT>
  struct apply
  {
    ReducingFnT step;
    IntegralT initial;

    template <typename StateT, typename ...InputTs>
    auto operator() (StateT&& s, InputTs&& ...is)
      -> decltype(wrap_state(step(state_unwrap(s), initial, is...), initial))
    {
      auto next  = state_data(std::forward<StateT>(s), constantly(initial));
      auto count = next++;
      return wrap_state(
        step(state_unwrap(std::forward<StateT>(s)),
             std::move(count),
             std::forward<InputTs>(is)...),
        std::move(next));
    }
  };
};

} // namespace detail

template <typename T>
using enumerate_t = transducer_impl<detail::enumerate_rf_gen, T>;

template <typename IntegralT>
constexpr auto enumerate_from(IntegralT&& init)
  -> enumerate_t<estd::decay_t<IntegralT> >
{
  return enumerate_t<estd::decay_t<IntegralT> > {
    std::forward<IntegralT>(init) };
}

extern const enumerate_t<std::size_t> enumerate;

#endif // ABL_CXX14

} // namespace xform
} // namespace atria