/*

 * This file is part of PowerDNS or dnsdist.

 * Copyright -- PowerDNS.COM B.V. and its contributors

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of version 2 of the GNU General Public License as

 * published by the Free Software Foundation.

 *

 * In addition, for the avoidance of any doubt, permission is granted to

 * link this program with OpenSSL and to (re)distribute the binaries

 * produced as the result of such linking.

 *

 * This program 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 General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program.

 */

#pragma once

#include <variant>

// A poor man's std::expected, which only becomes available for real with C++23

namespace pdns

{

template <class E>

class unexpected

{

public:

  explicit unexpected(const E& arg) :

    err(arg) {}

  const E& error() const

  {

    return err;

  }

private:

  E err;

};

template <class T, class E>

class expected : private std::variant<T, E>

{

public:

  expected(const T& arg) :

    std::variant<T, E>(arg) {}

  expected(T&& arg) :

    std::variant<T, E>(std::forward<T>(arg)) {}

  expected(const unexpected<E>& arg) :

    std::variant<T, E>(arg.error()) {}

  [[nodiscard]] bool has_value() const

  {

    return std::holds_alternative<T>(*this);

  }

  const T& value() const

  {

    return std::get<T>(*this);

  }

  const E& error() const

  {

    return std::get<E>(*this);

  }

};

}