GetHashCode

In the previous article, we talked a bit about hash codes and how they are implemented for reference types - it turned out that it’s just a simple multiplication of thread ID and a random number. Today, we will do the same thing for value types, which are far more complex due to their representation in memory. In the end, I will show a small benchmark to prove that every struct defined by the programmer should override GetHashCode method. Time to dig into CLR source code!

GetHashCode, a part of the Object class, is one of the key method present in every class instance. Its main purpose is to calculate and return a number associated with the specified object, which will be used as hash (a very good example is Dictionary class). This article will be split into two parts: the first one will focus on the reference types and the second one on the value types. We will focus on the internal implementation of CLR and try to figure out how exactly the hash code for reference and value types is generated.