third-party/mapbox/optional.hpp

//
// Copyright (c) MapBox All rights reserved.
// SPDX-License-Identifier: BSD-3-Clause
//

#ifndef MAPBOX_UTIL_OPTIONAL_HPP
#define MAPBOX_UTIL_OPTIONAL_HPP

#pragma message("This implementation of optional is deprecated. See https://github.com/mapbox/variant/issues/64.")

#include <type_traits>
#include <utility>

#include <mapbox/variant.hpp>

namespace mapbox {
namespace util {

template <typename T>
class optional
{
    static_assert(!std::is_reference<T>::value, "optional doesn't support references");

    struct none_type
    {
    };

    variant<none_type, T> variant_;

public:
    optional() = default;

    optional(optional const& rhs)
    {
        if (this != &rhs)
        { // protect against invalid self-assignment
            variant_ = rhs.variant_;
        }
    }

    optional(T const& v) { variant_ = v; }

    explicit operator bool() const noexcept { return variant_.template is<T>(); }

    T const& get() const { return variant_.template get<T>(); }
    T& get() { return variant_.template get<T>(); }

    T const& operator*() const { return this->get(); }
    T operator*() { return this->get(); }

    optional& operator=(T const& v)
    {
        variant_ = v;
        return *this;
    }

    optional& operator=(optional const& rhs)
    {
        if (this != &rhs)
        {
            variant_ = rhs.variant_;
        }
        return *this;
    }

    template <typename... Args>
    void emplace(Args&&... args)
    {
        variant_ = T{std::forward<Args>(args)...};
    }

    void reset() { variant_ = none_type{}; }

}; // class optional

} // namespace util
} // namespace mapbox

#endif // MAPBOX_UTIL_OPTIONAL_HPP