CODEWITHSUNDEEP
c#iterator
FLCL
FLCL

Reputation: 2514

GetEnumerator: return or yield return

My class implements IEnumerable. And these two ways to code GetEnumerator method can be compiled:

public IEnumerator GetEnumerator()
{
    yield return Database[id].GetEnumerator();
}

and

public IEnumerator GetEnumerator()
{
   return Database[DatabaseId].GetEnumerator();
}

where Database[id] is List. Is any difference between these implementations?

Upvotes: 2

Views: 739

Answers (1)

Marc Gravell
Marc Gravell

Reputation: 1062550

The reason that compiles is because you are being unclear what the enumerable is. If you make it generic it becomes more obvious:

public IEnumerator<Foo> GetEnumerator()
{
    return Database[id].GetEnumerator();
}

vs

public IEnumerator<IEnumerator<Foo>> GetEnumerator()
{
    yield return Database[id].GetEnumerator();
}

Your yield return version is not yielding the result: it is yielding the iterator - it is an iterator-of-iterators, an enumerator-of-enumerators. And not in a good way. Basically, "don't do that".

Upvotes: 6

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