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Questions tagged [gethashcode]

GetHashCode is method of base Object class of .Net Framework.

GetHashCode is method of base Object class of .Net Framework. A hash code is a numeric value that is used to identify an object during equality testing. It can also serve as an index for an object in a collection. The GetHashCode method is suitable for use in hashing algorithms and data structures such as a hash table.

Important notes

  • Equality of GetHashCode value doesn't necessarily imply equality of objects. The equality must be verified using Equals.
  • Inequality of GetHashCode necessarily means inequality of objects.
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Overriding GetHashCode

As you know, GetHashCode returns a semi-unique value that can be used to identify an object instance in a collection. As a good practice, it is recommended to override this method and implement your own. My question is - do you override this method…
Den
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String.GetHashCode() returns different values

Why is GetHashCode() returning a different value for the same string? I can't describe how to duplicate this, but trust that this is not a practical joke and that the two following lines came from my watch window at two separate…
Mark J Miller
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Using GetHashCode for getting Enum int value

I have an enum public enum INFLOW_SEARCH_ON { ON_ENTITY_HANDLE = 0, ON_LABEL = 1, ON_NODE_HANDLE = 2 } // enum INFLOW_SEARCH_ON I have to use this enum for searching in a grid column. To get the column…
Mohit Vashistha
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Overriding GetHashCode in VB without checked/unchecked keyword support?

So I'm trying to figure out how to correctly override GetHashCode() in VB for a large number of custom objects. A bit of searching leads me to this wonderful answer. Except there's one problem: VB lacks both the checked and unchecked keyword in…
Kumba
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implement GetHashCode() for objects that contain collections

Consider the following objects: class Route { public int Origin { get; set; } public int Destination { get; set; } } Route implements equality operators. class Routing { public List Paths { get; set; } } I used the code below to…
Joanna Derks
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What should GetHashCode return when object's identifier is null?

Which of the following is correct/better, considering that identity property could be null. public override int GetHashCode() { if (ID == null) { return base.GetHashCode(); } return ID.GetHashCode(); } OR public override int…
Dienekes
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Why is ValueType.GetHashCode() implemented like it is?

From ValueType.cs **Action: Our algorithm for returning the hashcode is a little bit complex. We look ** for the first non-static field and get it's hashcode. If the type has no ** non-static fields, we return the hashcode of the…
alh84001
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What is the difference between using IEqualityComparer and Equals/GethashCode Override?

When i am using dictionaries sometimes I have to change the default Equals meaning in order to compare Keys. I see that if I override the Equals and GetHashCode on the key's class or i create a new class which implements IEqualityComparer I have…
dariush624
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How to use System.HashCode.Combine with more than 8 values?

.NET Standard 2.1 / .NET Core 3 introduce System.HashCode to quickly combine fields and values to a hash code without having to care about the underlying implementation. However, it only provides Combine method overloads for up to 8 values. What do…
Ray
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Generate integer based on any given string (without GetHashCode)

I'm attempting to write a method to generate an integer based on any given string. When calling this method on 2 identical strings, I need the method to generate the same exact integer both times. I tried using .GetHasCode() however this is very…
mrb398
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Do I need to override GetHashCode() on reference types?

I read most questions on StackOverflow with regards to GetHashCode. But I am still not sure whether I have to override GetHashCode on reference types. I picked up the following from someones answer in another question: Object.GetHashCode() uses an…
user65199
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Why does C# not implement GetHashCode for Collections?

I am porting something from Java to C#. In Java the hashcode of a ArrayList depends on the items in it. In C# I always get the same hashcode from a List... Why is this? For some of my objects the hashcode needs to be different because the objects…
Peterdk
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GetHashCode on null fields?

How do I deal with null fields in GetHashCode function? Module Module1 Sub Main() Dim c As New Contact Dim hash = c.GetHashCode End Sub Public Class Contact : Implements IEquatable(Of Contact) Public Name As String Public…
Shimmy Weitzhandler
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C# how to calculate hashcode from an object reference

Folks, here's a thorny problem for you! A part of the TickZoom system must collect instances of every type of object into a Dictionary<> type. It is imperative that their equality and hash code be based on the instance of the object which means…
Wayne
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Overriding GetHashCode()

In this article, Jon Skeet mentioned that he usually uses this kind of algorithm for overriding GetHashCode(). public override int GetHashCode() { unchecked // Overflow is fine, just wrap { int hash = 17; // Suitable nullity checks etc,…
Pacane
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