C# Expression

1. 원래의 Singleton Instance 정의 

private static SystemCheckService instance;		
private static SystemCheckService Instance
{
	get
	{
		if (instance == null) instance = new SystemCheckService();
		return instance;
	}
}

 

2. Apply ?? Expression

private static SystemCheckService instance;
private static SystemCheckService Instance
{
	get { return instance ?? (instance = new SystemCheckService()); }
}

3. Apply Expression Body

private static SystemCheckService Instance => instance ?? (instance = new SystemCheckService());