C why gethashcode

Because it is distinct, the default comparison is the reference of the object… So this does not achieve our expected effect. Returns a non repeating element in a sequence by comparing values using the specified iequalitycomparer. If two equals return true and GetHashCode returns the same hash code, the two objects are considered equal.

The above is the whole content of this article, I hope to help you learn, and I hope you can support developer more. Posted 14 April and updated 12 June - 8 min read. Updated after I discovered that there is a new Nuget package called Microsoft.

HashCode which allows you to use System. HashCode in frameworks older than netstandard2. I updated this article to talk about a new HashCode class included in. NET Core 2. Implementing GetHashCode is hard work and little understood. If you take a look on MSDN or Stack Overflow for a few pointers, you'll see a plethora of examples with all kinds of little used C operators and magic numbers with little explanation for developers Especially the newbies what they are for and why we need them.

This, for a method which exists on the Object class and is the root of all that is good and wholesome in C is surprising. Before I continue, I recommend reading Eric Lippert's blog post about the subject. He does not show any code, just goes into when and where we need to implement the GetHashCode method.

Eric does a much better job than I could do but in short, GetHashCode is implemented wherever you implement the Equals method and ideally your class should be immutable. Now down to the nitty gritty. How do we make implementing GetHashCode easy. Well, suppose we have the following class:. In our example we have an immutable object with a variety of fields of different types, including a collection.

One possible implementation of GetHashCode according to the highest rated Stack Overflow post If modified to fit our example and deal with null 's may be:.

I don't know about you but that code looks awfully unwieldy to me. For a start we've got two different magic numbers 17 and As it happens these are prime numbers and reduces the chance of getting collisions between hashes Two un-equal objects are supposed to have different hash codes but sometimes this is not the case due to hash collisions that can occur.

We've also got the unchecked C keyword which stops overflow checking to improve performance That's not something you see every day. Show ;. Next C How to get the HashCode for the string. Recommended Articles. Article Contributed By :. Easy Normal Medium Hard Expert. Writing code in comment? Please use ide.

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