Re: List or Iterator

Lew <>
Fri, 24 Jul 2009 09:36:09 -0400
Adam Lipscombe wrote:

Are there any advantages in speed in passing a List or an Iterator as a
method parameter, or as a method return value?


Any runtime reasons why one should be preferred over the other?

Yes. Also design reasons.

Iterators don't like to share. Using one as a method parameter risks

It makes perfect sense to return an Iterator if the purpose of the method is
to obtain an iterator. Such a method should be an instance method of an
'Iterable' object.

It makes little if any sense to return an iterator that is not clearly tied to
such an object. Oh, I suppose one could manufacture a use case for such a
thing, but it would be at best a corner case, or else some sort of low-level
private or package-private implementation mechanism. Typically one would want
to return an 'Iterable' (which is therefore amenable to for-each looping) or

Iterators are by nature transitory, local things. Passing them around
willy-nilly will lead to bugs.


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