Why do arrays in .net only implement IEnumerable and not IEnumerable?

Question

I was implementing my own ArrayList class and was left surprised when I realised that

public System.Collections.Generic.IEnumerator GetEnumerator()          


        

Answer 1

You can use generic method IEnumerable<T> OfType<T>() from System.Linq namespace, which extends IEnumerable interface. It will filter out all elements which type is different than T and return IEnumerable<T> collection. If you use (IEnumerable<T>)_array conversion operator, it might not be safe, because System.Array (and other nongeneric types) stores items of type System.Object.

Answer 2

Arrays do implement IEnumerable<T>, but it is done as part of the special knowledge the CLI has for arrays. This works as if it were an explicit implementation (but isn't: it is done at runtime). Many tools will not show this implementation, this is described in the Remarks section of the Array class overview.

You could add a cast:

return ((IEnumerable<T>)_array).GetEnumerator();

Note, older MSDN (pre docs.microsoft.com) coverage of this changed a few times with different .NET versions, check for the remarks section.