Question

I probably miss something with array construction syntax in c#. If I have the following function (thanks to type variance feature in c# 4):

IEnumerable<IEnumerable<T>> test<T>()
{
        return new List<List<T>>();
}

How can I write similar one that instantiates array of array?

Answer 1

IEnumerable<IEnumerable<T>> test<T>()
{
        return new [] { new T[] {} };
}

_{I noticed that there used to be a bug in the mono compiler (at least, the 2.6.7 gmcs would crash…) that required you to spell new IEnumerable<T>[] { new T[] {}}; This is no longer a problem with e.g. mono 2.11}

Alternatively

you could use a yield block (which would be less efficient)

IEnumerable<IEnumerable<T>> test<T>()
{
        yield return new T[] {};
}

Enumerable.Empty<>

Are you aware of Enumerable.Empty<>?

IEnumerable<IEnumerable<T>> test<T>()
{
        return Enumerable.Empty<IEnumerable<T>>();
}