Question

I have writen about custom IEnumerator. Whats the simplest way to make IEnumerable from it ? Ideal solution (one line of code) would be if there was some class for that purpose. Or do I have to create my own ?

Answer 1

I would really approach this the other way around; while you can (as per Mike P’s excellent answer) wrap an enumerator to pretend to be enumerable, there are some things that you can’t really do – for example, it is hoped (although, to be fair, not insisted) that you can obtain multiple enumerators from an enumerable, ideally isolated and repeatable. So if I do:

Assert.AreEqual(sequence.Sum(), sequence.Sum());

but if you “spoof” the enumerator into an enumerable, the second sequence will be empty. Or if you do them in parallel – just bizarre. And there are methods that process them in parallel – consider:

Assert.IsTrue(sequence.SequenceEqual(sequence));

this works both enumerators forward at the same time, so if you only have one enumerator, you are fairly scuppered.

There is a reset on enumerators, but this is largely a design mistake and shouldn’t be used (it is even a formal requirement in the spec that iterator blocks throw an exception if you call it).

A better (IMO) question is “how do I get an enumerator from an enumerable”, in which case the answer is “call GetEnumerator(), and remember to check to dispose to iterator” – or in simpler terms “use foreach“.