with_state.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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#pragma once

#include <atria/xform/any_state.hpp>
#include <atria/meta/lazy_enable_if.hpp>

namespace atria {
namespace xform {

template <typename StateT,
          typename UnwrappedFn,
          typename WrappedFn>
auto with_state(StateT&& st, UnwrappedFn&&, WrappedFn&& fn)
  -> meta::lazy_enable_if_t<
    !std::is_same<
      estd::decay_t<StateT>,
      estd::decay_t<decltype(state_complete(st))>
    >::value,
    std::result_of<WrappedFn(StateT)>
  >
{
  return std::forward<WrappedFn>(fn)(std::forward<StateT>(st));
};

template <typename StateT,
          typename UnwrappedFn,
          typename WrappedFn>
auto with_state(StateT&& st, UnwrappedFn&& fn, WrappedFn&&)
  -> meta::lazy_enable_if_t<
    !std::is_same<estd::decay_t<StateT>, any_state>::value
    && std::is_same<
      estd::decay_t<StateT>,
      estd::decay_t<decltype(state_complete(st))>
    >::value,
    std::result_of<UnwrappedFn(StateT)>
  >
{
  return std::forward<UnwrappedFn>(fn)(std::forward<StateT>(st));
};

template <typename StateT,
          typename UnwrappedFn,
          typename WrappedFn>
auto with_state(StateT&& st, UnwrappedFn&& fn1, WrappedFn&& fn2)
  -> meta::lazy_enable_if_t<
    std::is_same<
      estd::decay_t<StateT>,
      any_state
    >::value,
    std::result_of<UnwrappedFn(StateT)>
  >
{
  using wrapped_state_t = estd::result_of_t<UnwrappedFn(StateT)>;

  if (!st.template has<wrapped_state_t>()) {
    return std::forward<UnwrappedFn>(fn1)(
      std::forward<StateT>(st));
  } else {
    return std::forward<WrappedFn>(fn2)(
      std::forward<StateT>(st).template as<wrapped_state_t>());
  }
};

} // namespace xform
} // namespace atria