mijin2/source/mijin/container/boxed_object.hpp

#pragma once

#if !defined(MIJIN_CONTAINER_BOXED_OBJECT_HPP_INCLUDED)
#define MIJIN_CONTAINER_BOXED_OBJECT_HPP_INCLUDED 1

#include <iterator>
#include <memory>
#include "../debug/assert.hpp"

namespace mijin
{

//
// public defines
//

#if !defined(MIJIN_BOXED_OBJECT_DEBUG)
#define MIJIN_BOXED_OBJECT_DEBUG MIJIN_DEBUG
#endif

//
// public constants
//

//
// public types
//

template<typename T>
class BoxedObject
{
private:
    union {
        std::byte placeholder_;
        T object_;
    };
#if MIJIN_BOXED_OBJECT_DEBUG
    bool constructed = false;
#endif
public:
    BoxedObject() noexcept : placeholder_() {};
    explicit BoxedObject(T object)
#if MIJIN_BOXED_OBJECT_DEBUG
    : constructed(true)
#endif
{
        std::construct_at(&object_, std::move(object));
    }
    BoxedObject(const BoxedObject&) = delete;
    BoxedObject(BoxedObject&&) = delete;

#if MIJIN_BOXED_OBJECT_DEBUG
    ~BoxedObject()
    {
        MIJIN_ASSERT(!constructed, "BoxedObject::~BoxedObject(): Object has not been destroyed prior to destructor!");
    }
#endif

    BoxedObject& operator=(const BoxedObject&) = delete;
    BoxedObject& operator=(BoxedObject&&) = delete;

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

    template<typename... TArgs>
    void construct(TArgs&&... args)
    {
#if MIJIN_BOXED_OBJECT_DEBUG
        MIJIN_ASSERT(!constructed, "BoxedObject::construct(): Attempt to construct an already constructed object!");
        constructed = true;
#endif
        std::construct_at(&object_, std::forward<TArgs>(args)...);
    }

    void destroy()
    {
#if MIJIN_BOXED_OBJECT_DEBUG
        MIJIN_ASSERT(constructed, "BoxedObject::destroy(): Attempt to destroy a not constructed object!");
        constructed = false;
#endif
        std::destroy_at(&object_);
    }
    
    void copyTo(BoxedObject& other) const
    {
#if MIJIN_BOXED_OBJECT_DEBUG
        MIJIN_ASSERT(constructed, "BoxedObject::copy(): Attempt to copy a not constructed object!");
#endif
        other.construct(object_);
    }

    void moveTo(BoxedObject& other)
    {
#if MIJIN_BOXED_OBJECT_DEBUG
        MIJIN_ASSERT(constructed, "BoxedObject::copy(): Attempt to copy a not constructed object!");
#endif
        other.construct(std::move(object_));
        destroy();
    }

    [[nodiscard]] T& get()
    {
#if MIJIN_BOXED_OBJECT_DEBUG
        MIJIN_ASSERT(constructed, "BoxedObject::get(): Attempt to access a not constructed object!");
#endif
        return object_;
    }

    [[nodiscard]] const T& get() const
    {
#if MIJIN_BOXED_OBJECT_DEBUG
        MIJIN_ASSERT(constructed, "BoxedObject::get(): Attempt to access a not constructed object!");
#endif
        return object_;
    }
};

template<typename T>
class BoxedObjectIterator
{
public:
    using difference_type = std::ptrdiff_t;
    using value_type = T;
private:
    BoxedObject<T>* box_ = nullptr;
#if MIJIN_CHECKED_ITERATORS
    BoxedObject<T>* start_ = nullptr;
    BoxedObject<T>* end_ = nullptr;
#endif
public:
    BoxedObjectIterator() = default;
    explicit constexpr BoxedObjectIterator(BoxedObject<T>* box, BoxedObject<T>* start, BoxedObject<T>* end)
        : box_(box)
#if MIJIN_CHECKED_ITERATORS
    , start_(start), end_(end)
#endif
    {}
    BoxedObjectIterator(const BoxedObjectIterator&) = default;
    BoxedObjectIterator(BoxedObjectIterator&&) noexcept = default;

    BoxedObjectIterator& operator=(const BoxedObjectIterator&) = default;
    BoxedObjectIterator& operator=(BoxedObjectIterator&&) noexcept = default;
    BoxedObjectIterator& operator+=(difference_type diff);
    BoxedObjectIterator& operator-=(difference_type diff) { return (*this += -diff); }

    constexpr auto operator<=>(const BoxedObjectIterator& other) const noexcept = default;

    [[nodiscard]] T& operator*() const;
    [[nodiscard]] T* operator->() const;
    BoxedObjectIterator& operator++();
    BoxedObjectIterator operator++(int);
    BoxedObjectIterator& operator--();
    BoxedObjectIterator operator--(int);

    [[nodiscard]] difference_type operator-(const BoxedObjectIterator& other) const { return box_ - other.box_; }
    [[nodiscard]] BoxedObjectIterator operator+(difference_type diff) const;
    [[nodiscard]] BoxedObjectIterator operator-(difference_type diff) const { return (*this + -diff); }

    [[nodiscard]] T& operator[](difference_type diff) const { return *(*this + diff); }
};
template<typename T>
inline BoxedObjectIterator<T> operator+(std::iter_difference_t<T> diff, const BoxedObjectIterator<T>& iter) {
    return iter + diff;
}
static_assert(std::random_access_iterator<BoxedObjectIterator<int>>);

//
// public functions
//

template<typename T>
BoxedObjectIterator<T>& BoxedObjectIterator<T>::operator+=(difference_type diff)
{
#if MIJIN_CHECKED_ITERATORS
    MIJIN_ASSERT(diff <= (end_ - box_) && diff >= (box_ - start_), "BoxedObjectIterator::operator+=(): Attempt to iterate out of range.");
#endif
    box_ += diff;
    return *this;
}

template<typename T>
T& BoxedObjectIterator<T>::operator*() const
{
#if MIJIN_CHECKED_ITERATORS
    MIJIN_ASSERT(box_ >= start_ && box_ < end_, "BoxedObjectIterator::operator->(): Attempt to dereference out-of-range iterator.");
#endif
    return box_->get();
}

template<typename T>
BoxedObjectIterator<T>& BoxedObjectIterator<T>::operator++()
{
#if MIJIN_CHECKED_ITERATORS
    MIJIN_ASSERT(box_ < end_, "BoxedObjectIterator::operator++(): Attempt to iterator past the end.");
#endif
    ++box_;
}

template<typename T>
BoxedObjectIterator<T> BoxedObjectIterator<T>::operator++(int)
{
#if MIJIN_CHECKED_ITERATORS
    MIJIN_ASSERT(box_ < end_, "BoxedObjectIterator::operator++(int): Attempt to iterator past the end.");
#endif
    BoxedObjectIterator copy(*this);
    ++box_;
    return copy;
}

template<typename T>
BoxedObjectIterator<T>& BoxedObjectIterator<T>::operator--()
{
#if MIJIN_CHECKED_ITERATORS
    MIJIN_ASSERT(box_ > start_, "BoxedObjectIterator::operator--(): Attempt to iterator past start.");
#endif
    --box_;
}

template<typename T>
BoxedObjectIterator<T> BoxedObjectIterator<T>::operator--(int)
{
#if MIJIN_CHECKED_ITERATORS
    MIJIN_ASSERT(box_ > start_, "BoxedObjectIterator::operator--(int): Attempt to iterator past start.");
#endif
    BoxedObjectIterator copy(*this);
    --box_;
    return copy;
}

template<typename T>
BoxedObjectIterator<T> BoxedObjectIterator<T>::operator+(difference_type diff) const
{
    BoxedObjectIterator copy(*this);
    copy += diff;
    return copy;
}

} // namespace mijin

#endif // !defined(MIJIN_CONTAINER_BOXED_OBJECT_HPP_INCLUDED)