ResourceHolder.h

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/*******************************************************************************
 * Copyright (C) 2017-2025 Theodore Chang
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * 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.  If not, see <http://www.gnu.org/licenses/>.
 ******************************************************************************/
#ifndef RESOURCEHOLDER_H
#define RESOURCEHOLDER_H
 
#include <memory>
 
template<typename T> requires requires(T* copyable) { copyable->get_copy(); }
class ResourceHolder final {
    std::unique_ptr<T> object = nullptr;
 
public:
    ResourceHolder() = default;
 
    ResourceHolder(const ResourceHolder& old_holder)
        : object(old_holder ? old_holder.object->get_copy() : nullptr) {}
 
    ResourceHolder(ResourceHolder&& old_holder) noexcept { object = std::move(old_holder.object); }
 
    ResourceHolder& operator=(const ResourceHolder&) = delete;
    ResourceHolder& operator=(ResourceHolder&&) = delete;
    ~ResourceHolder() = default;
 
    explicit ResourceHolder(std::unique_ptr<T>&& original_object)
        : object(std::move(original_object)) {}
 
    template<typename U> requires std::is_base_of_v<T, U> ResourceHolder& operator=(U&& other) {
        object = std::make_unique<U>(std::forward<U>(other));
        return *this;
    }
 
    ResourceHolder& operator=(const std::shared_ptr<T>& original_object) {
        if(nullptr != original_object) object = original_object->get_copy();
        return *this;
    }
 
    T* operator->() const { return object.get(); }
 
    explicit operator bool() const { return object != nullptr; }
 
    bool operator==(const ResourceHolder& other) const { return object == other.object; }
 
    bool operator==(const T& other) const { return object == other; }
 
    bool operator==(std::nullptr_t null) const { return object == null; }
};
 
#endif