[stringtemplate-interest] Bug in rest function when applied recursively

[Zenaan Harkness]

On Thu, Sep 28, 2006 at 03:02:50PM -0400, John Snyders wrote:
> I was thinking about how templates can be called recursively. Just for fun I
> decided to try the classic recursive definition of reverse.
>     group Reverse;
>     reverse(L) ::= <<
>     $if(L)$
>     $reverse(rest(L))$$first(L)$
>     $endif$
>     >>
...
> I changed rest to return a new collection (ArrayList) that contains the rest
> of the original collection. After making this change the reverse template
> worked perfectly.
> 
> The trouble is that creating a new collection is wasteful. Perhaps there is
> a way to determine if a copy of rest is needed rather than just an iterator.
> For example just at the point where the iterator is going to be passed to a
> template it is copied to a new collection. Are there any other cases where
> an iterator should be turned to a collection?
> 
> If Java iterators supported cloning (clone would create a new iterator over
> the same colection positioned at the point where the original iterator was
> cloned) it may be enough to always return a cloned iterator from rest. But
> Java iterators don?t allow cloning.

Create a CloneableArrayListIterator, etc (or whatever iterators
are needed).

It's only the built-in iterators which don't support cloning, of
course :)

Cloning the iterator sounds like it might not introduce too much
of a performance hit.

Creating a new collection does sound awefully heavy...

cheers
zen

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