Future.h

/*****************************************************************************
 * vim:tw=78
 *
 * Copyright (C) 2022 Bjarne von Horn (vh at igh dot de).
 *
 * This file is part of the PdCom library.
 *
 * The PdCom library is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or (at your
 * option) any later version.
 *
 * The PdCom library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with the PdCom library. If not, see <http://www.gnu.org/licenses/>.
 *
 *****************************************************************************/

#ifndef PDCOM5_FUTURE_H
#define PDCOM5_FUTURE_H

#include "pdcom5_export.h"

#include <functional>
#include <memory>

namespace PdCom {
namespace impl {
template <class Exception, class... Result>
struct Promise;
}

template <class Exception, class... Result>
class PDCOM5_PUBLIC Future
{
  public:
    using ResolveFn = std::function<void(Result...)>;
    using RejectFn  = std::function<void(Exception)>;

    Future() = default;
    Future(std::shared_ptr<impl::Promise<Exception, Result...>> impl) noexcept :
        impl_(std::move(impl))
    {}
    Future(Future &&)                 = default;
    Future(const Future &)            = delete;
    Future &operator=(Future &&)      = default;
    Future &operator=(const Future &) = delete;

    const Future &then(ResolveFn resolve) const &;
    Future then(ResolveFn resolve) &&;
    const Future &handle_exception(RejectFn reject) const &;
    Future handle_exception(RejectFn reject) &&;

    bool empty() const noexcept { return !impl_.operator bool(); }

    struct Hash
    {
        std::size_t operator()(Future const &future) const
        {
            return std::hash<
                    std::shared_ptr<impl::Promise<Exception, Result...>>>()(
                    future.impl_);
        }
    };

    struct Less
    {
        bool operator()(const Future &lhs, const Future &rhs) const noexcept
        {
            return std::owner_less<
                    std::shared_ptr<impl::Promise<Exception, Result...>>>()(
                    lhs.impl_, rhs.impl_);
        }
    };

    bool operator==(const Future &other) const noexcept
    {
        return other.impl_ == impl_;
    }

  private:
    std::shared_ptr<impl::Promise<Exception, Result...>> impl_;
};
}  // namespace PdCom

namespace std {
template <class Exception, class... Result>
struct hash<PdCom::Future<Exception, Result...>> :
    PdCom::Future<Exception, Result...>::Hash
{};

template <class Exception, class... Result>
struct less<PdCom::Future<Exception, Result...>> :
    PdCom::Future<Exception, Result...>::Less
{};

}  // namespace std


#endif  // PDCOM5_FUTURE_H