有效的C＃：覆盖Object.Equals（），不管是不是？

Question

In the second edition of Effective C# (ISBN-13: 978-0321658708) on page 37, the book reads

The second function you'll never redefine is static Object.Equals()

However, on page 39, the book reads

The point is that if your type should follow value semantics (comparing contents) instead of reference semantics (comparing object identity), you should write your own override of instance Object.Equals()

Would someone be so kind as to explain why one would override

public virtual bool Equals(object right);

and not

public static bool Equals(object left, object right);

Thank you :)

Answer 1

因为您无法覆盖静态方法。

Answer 2

The first thing to clear is you cannot override static methods. The implementation of

public static bool Equals(object left, object right);

cannot be overridden. The static equals method is only for connivence for not doing a null check. Internally it first checks for reference equals and then content equals(non static equals method).

In the quotes you mentioned above, the first quote refers the static equals method where as second refers non static equals method both are written in notation as Object.Equals() but notice that the first one says "static Object.Equals()"

Answer 3

never redefine static Object.Equals()

You should write your own override of instance Object.Equals()

Notice the difference, static vs instance . These sentences are not referring to the same method...

Answer 4

另外，如果我没有弄错的话，静态的只会比较参考，其中虚拟的那个使你能够编写自己的比较，大多数时候都是基于值而不是参考。