match_eggs.hpp

Go to the documentation of this file.

//
// Copyright (C) 2014, 2015 Ableton AG, Berlin. All rights reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// 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
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//

#pragma once

#include <atria/variant/variant_types_eggs.hpp>
#include <atria/variant/visitor.hpp>

#include <ableton/build_system/Warnings.hpp>
ABL_DISABLE_WARNINGS
#include <eggs/variant.hpp>
ABL_RESTORE_WARNINGS
#include <utility>

namespace atria {
namespace variant {

namespace detail {

template <typename T>
struct is_eggs_variant : std::is_base_of<
  meta::unpack<eggs::variant, variant_types_t<estd::decay_t<T> > >,
  estd::decay_t<T> >
{};

} // namespace detail

template <typename VariantT, typename ...FnTs>
auto match(VariantT&& variant, FnTs&& ...fns)
  -> estd::enable_if_t<
  detail::is_eggs_variant<estd::decay_t<VariantT> >{},
    visitor_result_of_t<
      detail::visitor_impl<FnTs...>,
      variant_types_t<VariantT&&> > >
{
  using result_t = visitor_result_of_t<
    detail::visitor_impl<FnTs...>,
    variant_types_t<VariantT&&> >;

  using eggs_t = meta::copy_decay_t<
    VariantT,
    meta::unpack<eggs::variant, variant_types_t<estd::decay_t<VariantT> > > >;

  return eggs::variants::apply<result_t>(
    visitor_for<VariantT>(std::forward<FnTs>(fns)...),
    // eggs::variants::apply is too stupid to detect that a subclass
    // of a variant can be destructured, so we cast up such that
    // subclassing works
    std::forward<eggs_t>(static_cast<eggs_t&&>(variant)));
}

} // namespace variant
} // namespace atria