public class MyClass
{
	public int ID;


    /*public static bool operator ==(MyClass c1, MyClass c2)
    {
        //下面這段程式碼中的“==”呼叫會進入遞迴，直至崩潰
        if (c1 == null || c2 == null)
        {
            return c1 == c2;
        }


        return c1.ID == c2.ID;
    }


    public static bool operator !=(MyClass c1, MyClass c2)
    {
        //下面這段程式碼中的“==”呼叫會進入遞迴，直至崩潰
        if (c1 == null || c2 == null)
        {
            return c1 != c2;
        }


        return c1.ID != c2.ID;
    }*/
    
    //正確的方法
    public static bool operator ==(MyClass c1, MyClass c2)
    {
        //將c1物件轉為object再進行判斷
        //這裡的object.Equals(c1, null)也可以寫成
        //c1 as object == null
        if (object.Equals(c1, null) || object.Equals(c2, null))
        {
            return object.Equals(c1, c2);
        }


        return c1.ID == c2.ID;
    }


    public static bool operator !=(MyClass c1, MyClass c2)
    {
        if (object.Equals(c1, null) || object.Equals(c2, null))
        {
            return !object.Equals(c1, c2);
        }


        return c1.ID != c2.ID;
    }
}