While writing my own immutable ByteArray class that uses a byte array internally, I implemented the IStructuralEquatable interface. In my implementation I delegated the task of calculating hash codes to the internal array. While testing it, to my great surprise, I found that my two different arrays had the same structural hash code, i.e. they returned the same value from GetHashCode. To reproduce:
IStructuralEquatable array11 = new int[] { 1, 1 };
IStructuralEquatable array12 = new int[] { 1, 2 };
IStructuralEquatable array22 = new int[] { 2, 2 };
var comparer = EqualityComparer<int>.Default;
Console.WriteLine(array11.GetHashCode(comparer)); // 32
Console.WriteLine(array12.GetHashCode(comparer)); // 32
Console.WriteLine(array22.GetHashCode(comparer)); // 64
IStructuralEquatable is quite new and unknown, but I read somewhere that it can be used to compare the contents of collections and arrays. Am I wrong, or is my .Net wrong?
Note that I am not talking about Object.GetHashCode!
Edit:
So, I am apparently wrong as unequal objects may have equal hash codes. But isn't GetHashCode returning a somewhat randomly distributed set of values a requirement? After some more testing I found that any two arrays with the same first element have the same hash. I still think this is strange behavior.