Generic IEqualityComparer and GetHashCode

Question

Being somewhat lazy about implementing lots of IEqualityComparers, and given that I couldn\'t easily edit class implementations of object being compared, I went with the fol

Answer 1

Your performance will go down the drain. Distinct and Except are efficient operations when implemented on set data structures. By providing a constant hash value you essentially destroy this characteristic and force naive algorithm using a linear search.

You need to see whether this is acceptable for your data volume. But for somewhat larger data sets, the difference will be pronounced. For example, Except will increase from expected time O(n) to O(n²), which can be a big deal.

Rather than providing a constant, why not just call the object’s own GetHashCode method? It may not give a particularly good value but it cannot be worse than using a constant, and correctness will still be preserved unless the GetHashCode method of the object is overridden to return wrong values.