Return all enumerables with yield return at once; without looping through

Question

I have the following function to get validation errors for a card. My question relates to dealing with GetErrors. Both methods have the same return type IEnumerable&

Answer 1

You could set up all the error sources like this (method names borrowed from Jon Skeet's answer).

private static IEnumerable> GetErrorSources(Card card)
{
    yield return GetMoreErrors(card);
    yield return GetOtherErrors();
    yield return GetValidationErrors();
    yield return AnyMoreErrors();
    yield return ICantBelieveHowManyErrorsYouHave();
}

You can then iterate over them at the same time.

private static IEnumerable GetErrors(Card card)
{
    foreach (var errorSource in GetErrorSources(card))
        foreach (var error in errorSource)
            yield return error;
}

Alternatively you could flatten the error sources with SelectMany.

private static IEnumerable GetErrors(Card card)
{
    return GetErrorSources(card).SelectMany(e => e);
}

The execution of the methods in GetErrorSources will be delayed too.