Sized

[Brian Goetz]

Iterable doesn't guarantee that you can iterate the source more than once.  It is entirely consistent with the Iterable spec that iterator() always returns the same Iterator.  

On Nov 4, 2012, at 10:31 AM, Kevin Bourrillion wrote:

> On Fri, Nov 2, 2012 at 3:53 PM, Brian Goetz <brian.goetz at oracle.com> wrote:
> 
> I think you're focusing on another problem.  These things *have* size() methods already; I'm trying to capture this in a finer-grained interface.  The "size in O(1) time" is a whole orthogonal concern.
> 
> Sorry -- I was just going off the initial description, "It is useful to indicate that an aggregate knows its size."  If the real goal instead is only to distinguish when an aggregate "decides to expose a size() operation for whatever reason", then right, there's no problem here.
> 
> But this new understanding doesn't make clear the reason why Iterable shouldn't go ahead and extend Sized as well. As Mike says, it "can determine it's size and that size() implementation is at least as good as getting an iterator and counting the items" -- that's undeniably the case. And as you say, the performance question is orthogonal.
> 
> But I think you don't want that, so I am still missing what the distinction between Sized and not Sized is supposed to be.
> 
> 
> -- 
> Kevin Bourrillion | Java Librarian | Google, Inc. | kevinb at google.com
>