pybind11/example/object.h

#if !defined(__OBJECT_H)
#define __OBJECT_H

#include <atomic>

/// Reference counted object base class
class Object {
public:
    /// Default constructor
    Object() { }

    /// Copy constructor
    Object(const Object &) : m_refCount(0) {}

	/// Return the current reference count
	int getRefCount() const { return m_refCount; };

	/// Increase the object's reference count by one
	void incRef() const { ++m_refCount; }

	/** \brief Decrease the reference count of
	 * the object and possibly deallocate it.
	 *
	 * The object will automatically be deallocated once
	 * the reference count reaches zero.
	 */
	void decRef(bool dealloc = true) const {
	    --m_refCount;
	    if (m_refCount == 0 && dealloc)
            delete this;
        else if (m_refCount < 0)
	        throw std::runtime_error("Internal error: reference count < 0!");
    }

    virtual std::string toString() const = 0;
protected:
	/** \brief Virtual protected deconstructor.
	 * (Will only be called by \ref ref)
	 */
	virtual ~Object() { }
private:
    mutable std::atomic<int> m_refCount { 0 };
};

/**
 * \brief Reference counting helper
 *
 * The \a ref refeference template is a simple wrapper to store a
 * pointer to an object. It takes care of increasing and decreasing
 * the reference count of the object. When the last reference goes
 * out of scope, the associated object will be deallocated.
 *
 * \ingroup libcore
 */
template <typename T> class ref {
public:
	/// Create a nullptr reference
    ref() : m_ptr(nullptr) { std::cout << "Created empty ref" << std::endl; }

    /// Construct a reference from a pointer
	ref(T *ptr) : m_ptr(ptr) {
        std::cout << "Initialized ref from pointer " << ptr<< std::endl;
	    if (m_ptr) ((Object *) m_ptr)->incRef();
	}

	/// Copy constructor
    ref(const ref &r) : m_ptr(r.m_ptr) {
        std::cout << "Initialized ref from ref " << r.m_ptr << std::endl;
        if (m_ptr)
            ((Object *) m_ptr)->incRef();
    }

    /// Move constructor
    ref(ref &&r) : m_ptr(r.m_ptr) {
        std::cout << "Initialized ref with move from ref " << r.m_ptr << std::endl;
        r.m_ptr = nullptr; 
    }

    /// Destroy this reference
    ~ref() {
        std::cout << "Destructing ref " << m_ptr << std::endl;
        if (m_ptr)
            ((Object *) m_ptr)->decRef();
    }

    /// Move another reference into the current one
	ref& operator=(ref&& r) {
        std::cout << "Move-assigning ref " << r.m_ptr << std::endl;
		if (*this == r)
			return *this;
		if (m_ptr)
			((Object *) m_ptr)->decRef();
		m_ptr = r.m_ptr;
		r.m_ptr = nullptr;
		return *this;
	}

	/// Overwrite this reference with another reference
	ref& operator=(const ref& r) {
        std::cout << "Assigning ref " << r.m_ptr << std::endl;
		if (m_ptr == r.m_ptr)
			return *this;
		if (m_ptr)
			((Object *) m_ptr)->decRef();
		m_ptr = r.m_ptr;
		if (m_ptr)
			((Object *) m_ptr)->incRef();
		return *this;
	}

	/// Overwrite this reference with a pointer to another object
	ref& operator=(T *ptr) {
        std::cout << "Assigning ptr " << ptr << " to ref" << std::endl;
		if (m_ptr == ptr)
			return *this;
		if (m_ptr)
			((Object *) m_ptr)->decRef();
		m_ptr = ptr;
		if (m_ptr)
			((Object *) m_ptr)->incRef();
		return *this;
	}

	/// Compare this reference with another reference
	bool operator==(const ref &r) const { return m_ptr == r.m_ptr; }

	/// Compare this reference with another reference
	bool operator!=(const ref &r) const { return m_ptr != r.m_ptr; }

	/// Compare this reference with a pointer
	bool operator==(const T* ptr) const { return m_ptr == ptr; }

	/// Compare this reference with a pointer
	bool operator!=(const T* ptr) const { return m_ptr != ptr; }

	/// Access the object referenced by this reference
	T* operator->() { return m_ptr; }

	/// Access the object referenced by this reference
	const T* operator->() const { return m_ptr; }

	/// Return a C++ reference to the referenced object
	T& operator*() { return *m_ptr; }

	/// Return a const C++ reference to the referenced object
	const T& operator*() const { return *m_ptr; }

	/// Return a pointer to the referenced object
	operator T* () { return m_ptr; }

	/// Return a const pointer to the referenced object
	T* get() { return m_ptr; }

	/// Return a pointer to the referenced object
	const T* get() const { return m_ptr; }
private:
	T *m_ptr;
};

#endif /* __OBJECT_H */