test-example-projects/c++_projects/84wsoui3/utilities/include/helper/SEmptyable.hpp

#pragma once
namespace SOUI
{

	/**
	* This is an type which can represent an value or NULL.
	* For example "SEmptyable<int> func();" means this function can return an int or nothing.
	*
	* Code example:
	*      Emptyable<int> a = 3;
	*      Emptyable<int> b(4);
	*      a = 4;
	*      assert(!a.isEmpty());
	*/
	template <class T>
	class SEmptyable
	{
	public:
		SEmptyable(T val)
			: m_val(val), m_empty(false)
		{

		}

		SEmptyable()
			: m_empty(true)
		{
		}

		bool isEmpty() const
		{
			return m_empty;
		}

		bool operator==(const SEmptyable &right) const
		{
			if (this->isEmpty() != right.isEmpty())
			{
				return false;
			}

			// both is empty.
			if (this->isEmpty())
			{
				return true;
			}

			return this->m_val == right.m_val;
		}

		bool operator==(const T &right) const
		{
			if (this->isEmpty())
			{
				return false;
			}

			return this->m_val == right;
		}


		bool operator!=(const SEmptyable &right) const
		{
			return !(operator==(right));
		}

		bool operator!=(const T &right) const
		{
			return !(operator==(right));
		}

		bool operator<(const SEmptyable &right) const
		{
			if (this->isEmpty() != right.isEmpty())
			{
				return this->isEmpty();
			}

			if (this->isEmpty())
			{
				return false;
			}

			return this->m_val < right.m_val;
		}

		bool operator<(const T &right) const
		{
			if (this->isEmpty())
			{
				return true;
			}

			return this->m_val < right;
		}

		SEmptyable &operator=(const SEmptyable &right)
		{
			m_val = right.m_val;
			m_empty = right.m_empty;
			return *this;
		}

		SEmptyable &operator=(const T &val)
		{
			m_val = val;
			m_empty = false;
			return *this;
		}

		operator T() const
		{
			assert(m_empty == false);
			return m_val;
		}

		void reset()
		{
			m_empty = true;
		}

	private:
		T m_val;
		bool m_empty;
	};
}