Which .Equals() method to use

Question

In this question. we discovered that in .NET 1.1, Array.IndexOf(array, value) searched for an element with

value.Equals(arrayElement) == true

while .NET 2.0 changed it to search for an element with

arrayElement.Equals(value) == true

Obviously the potential difference between the two results arises from polymorphism, but is there any reason why the latter version is preferable? More generally, if I have two objects a and b to compare, is there any good reason to prefer a.Equals(b) or b.Equals(a)?

Answer 1

I guess this is done to avoid problems when you override Equals in object you're feeding into IndexOf. In other words, if you have class Foo with some weird Equals implementation, this:

Foo f = new Foo();
Bar b = arrayOfDateTimes.IndexOf(f);

could potentially disrupt the behavior and yield strange results.

Answer 2

Just a guess, but the 1.1 version may have had a higher rate of NullReferenceExceptions compared to the 2.0 version.