重写Equals():调用base.Equals()时是否为空冗余比较？

Question

覆盖该Equals()方法时,MSDN建议:

class Point: Object {
   protected int x, y;

   public Point(int X, int Y) {
      this.x = X;
      this.y = Y;
   }

   public override bool Equals(Object obj) {

      //Check for null and compare run-time types.
      if (obj == null || GetType() != obj.GetType()) return false;

      Point p = (Point)obj;

      return (x == p.x) && (y == p.y);
   }
}

但是如果我们知道子类直接继承自的Object,那么下面是等价的吗？请注意!base.Equals()电话:

class Point: Object {
   protected int x, y;

   public Point(int X, int Y) {
      this.x = X;
      this.y = Y;
   }

   public override bool Equals(Object obj) {

      if (!base.Equals(obj) || GetType() != obj.GetType()) return false;

      Point p = (Point)obj;

      return (x == p.x) && (y == p.y);
   }
}

Answer 1

如果this引用是null对的,那么检查可以(但似乎不能保证)是多余的,如本答案中RuntimeHelpers.Equals引用的实现中所示.

但是,!base.Equals(obj)支票会打破你的Equals.如果引用不是null- !base.Equals也true将为任何不同的引用产生,不仅仅是null值.

出现问题的情况是:

Point x = new Point(1,2);
Point y = new Point(1,2);

Console.WriteLine(x.Equals(y));  // will print 'False'

尽管x并且y在业务逻辑方面是相同的,但它们是不同的对象,因此base.Equal返回false.