Why does C# not implement GetHashCode for Collections?

c# java collections hashcode gethashcode
Peterdk picture Peterdk · May 25, 2010 · Viewed 10.6k times · Source

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 in their list property make the objects non-equal. I would expect that a hashcode is always unique for the object's state and only equals another hashcode when the object is equal. Am I wrong?

Answer

SLaks picture SLaks · May 26, 2010

In order to work correctly, hashcodes must be immutable – an object's hash code must never change.

If an object's hashcode does change, any dictionaries containing the object will stop working.

Since collections are not immutable, they cannot implement GetHashCode.
Instead, they inherit the default GetHashCode, which returns a (hopefully) unique value for each instance of an object. (Typically based on a memory address)

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