owner_ptr.h

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#ifndef KUT_OWNERPTR_H
#define KUT_OWNERPTR_H
#pragma once

#include <cassert>
#include <utility>
#include <type_traits>

namespace kut
{
	//Based on Corrade's Pointer but with some differences
	//https://github.com/mosra/corrade/blob/master/src/Corrade/Containers/Pointer.h

	template<typename T>
	class owner_ptr
	{
		//Don't use/allow this class for arrays
		static_assert(!std::is_array<T>::value, "owner_ptr cannot refer to arrays");
		//Used in the move constructors for convertible types
		template<typename U> friend class owner_ptr;

	public:
		//Some typedefs to match unique_ptr, I don't bother to use them internally
		using pointer = T*;
		using element_type = T;
		
		//implicit construction of null pointer
		owner_ptr(std::nullptr_t = nullptr) noexcept : _p() {}
		//explicit construction with a pointer value
		explicit owner_ptr(T* p) noexcept : _p(p) {}

		//copy constructor is deleted
		owner_ptr(const owner_ptr<T>&) = delete;
		//move constructor
		template<typename U>
		owner_ptr(owner_ptr<U>&& other) noexcept : _p(static_cast<T*>(other._p))
		{
			other._p = nullptr;
		}

		//assignment copy is deleted
		owner_ptr<T>& operator=(const owner_ptr<T>&) = delete;
		//move assignment
		template<typename U>
		owner_ptr<T>& operator=(owner_ptr<U>&& other) noexcept
		{
			//swap our pointers
			auto temp = other._p;
			other._p = static_cast<U*>(_p);
			_p = static_cast<T*>(temp);
		}

		//comparisons to null pointer
		bool operator==(std::nullptr_t) const noexcept { return _p == nullptr; }
		bool operator!=(std::nullptr_t) const noexcept { return _p != nullptr; }

		//destructor
		~owner_ptr() { delete _p; }

		//bool conversion to check validity
		explicit operator bool() const noexcept { return _p; }

		//retrieve underlying pointer
		T* get() noexcept { return _p; }
		const T* get() const noexcept { return _p; }

		//call through to pointer object
		T* operator->() noexcept
		{
			assert(_p);
			return _p;
		}

		const T* operator->() const noexcept
		{
			assert(_p);
			return _p;
		}

		//dereference to underlying object
		T& operator*() noexcept
		{
			assert(_p);
			return _p;
		}

		const T& operator*() const noexcept
		{
			assert(_p);
			return _p;
		}

		//clear out the pointer
		void reset(T* pointer = nullptr) noexcept
		{
			delete _p;
			_p = pointer;
		}

		T* release() noexcept
		{
			auto ptr = _p;
			_p = nullptr;
			return ptr;
		}

	private:
		T* _p;
	};

	//reverse equality comparisons
	template<typename T> bool operator==(std::nullptr_t, const owner_ptr<T>& p) { return p == nullptr; }
	template<typename T> bool operator!=(std::nullptr_t, const owner_ptr<T>& p) { return p != nullptr; }

	//make_unique equivalent, construct pointer and underlying object
	template<typename T, typename... Args>
	inline owner_ptr<T> make_owner(Args&&... args)
	{
		return owner_ptr<T>(new T(std::forward<Args>(args)...));
	}
}

#endif