blocks|key|343521|text|当你覆盖Equals的时候，基本上。当您希望提供与简单引用相等不同的相等概念时。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|343522|String就是一个很好的例子--如果两个字符串代表相同的字符序列，那么它们是相等的(在一个简单的Equals调用下)。散列代码反映了这一点，因此如果两个字符串相等，则它们将具有相同的散列代码。(反之亦然--两个不相等的字符串可以有相同的哈希码，但这不太可能。)|343523|(请注意，字符串在其他方面也很棘手--基于区域性和大小写有许多不同的相等概念，但String.Equals只查看组成字符串的UTF-16代码点，并以最简单的方式对它们进行比较。)|343524|entityMap^0|4|6|0|0|14|D|0^^$0|@$1|2|3|4|5|6|7|L|8|@$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|P|8|@$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|J|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|K|$]]

When you override <code>Equals</code>, basically. When you want to provide a different idea of equality than simple reference equality.

String is a good example of this - two strings are equal (under a simple Equals call) if they represent the same sequence of characters. The hash code reflects this, such that if two strings are equal they will have the same hash code. (The reverse isn't necessarily true - two unequal strings can have the same hash code, but it's unlikely.)

(Strings are tricky in other ways, mind you - there are lots of different ideas of equality based on culture and casing, but <code>String.Equals</code> just looks at the UTF-16 code points which make up the string, and compares them in the simplest conceivable fashion.)

blocks|key|3332529|text|如果覆盖Equals，则还必须覆盖GetHashCode。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3332530|entityMap^0|4|6|H|B|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

If you override <code>Equals</code> you must override <code>GetHashCode</code> as well.

blocks|key|343554|text|“派生类型可以重写GetHashCode方法。值类型必须重写此方法以提供适用于该类型的哈希函数，并在哈希表中提供有用的分布。为了获得最佳结果，哈希代码必须基于实例字段或属性的值，而不是基于静态字段或属性。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|343555|在Hashtable对象中用作键的对象也必须覆盖GetHashCode方法，因为这些对象必须生成自己的散列代码。如果用作键的对象不提供有用的GetHashCode实现，则可以在构造哈希表对象时指定哈希码提供程序。在.NET框架2.0版之前，散列代码提供程序是基于System.Collections..::.IHashCodeProvider接口的。从2.0版开始，哈希码提供程序基于System.Collections..::.IEqualityComparer接口。“|343556|http://msdn.microsoft.com/en-us/library/system.object.gethashcode.aspx|offset|length|343557|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|0|1Y|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Q|8|@]|9|@$F|R|G|S|1|T]]|A|$]]|$1|H|3|-4|5|6|7|U|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|E]]]]

"The GetHashCode method can be overridden by a derived type. Value types must override this method to provide a hash function that is appropriate for that type and to provide a useful distribution in a hash table. For best results, the hash code must be based on the value of an instance field or property instead of a static field or property.

Objects used as a key in a Hashtable object must also override the GetHashCode method because those objects must generate their own hash code. If an object used as a key does not provide a useful implementation of GetHashCode, you can specify a hash code provider when the Hashtable object is constructed. Prior to the .NET Framework version 2.0, the hash code provider was based on the System.Collections..::.IHashCodeProvider interface. Starting with version 2.0, the hash code provider is based on the System.Collections..::.IEqualityComparer interface."

<a href="http://msdn.microsoft.com/en-us/library/system.object.gethashcode.aspx" rel="nofollow noreferrer">http://msdn.microsoft.com/en-us/library/system.object.gethashcode.aspx</a>

blocks|key|3120197|text|如果您的类型应该遵循值语义(比较内容)而不是引用语义(比较对象标识)，那么您应该编写自己的实例object.Equals()覆盖。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3120198|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

If your type should follow value semantics (comparing contents) instead of reference semantics (comparing object identity) , you should write you own override of instance object.Equals().

When should we override the GetHashCode() method provided by 'Object' class in 'System' namespace?

When to override GetHashCode()?

哈希函数

我们应该在什么时候覆盖由‘System’命名空间中的‘Object’类提供的GetHashCode()方法？

问什么时候重写GetHashCode()？
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