Using GetHashCode correctly

For reference types, the hash is based on an internal counter that is incremented every time a descendant of System.Object is created. This happens in System.Object's constructor.

For value types (structs), the hash is based on the first field. So if the first field is immutable, then you don't have to overload GetHashCode for your type since the hash based on it will never change.

Source: Bill Wagner's Effective C# (first edition).