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RE: [xsl] [XSLT Streaming] Are xsl:for-each and xsl:iterate equivalent?


Subject: RE: [xsl] [XSLT Streaming] Are xsl:for-each and xsl:iterate equivalent?
From: "Costello, Roger L." <costello@xxxxxxxxx>
Date: Thu, 29 Aug 2013 13:37:47 +0000

Thanks David, this is excellent.

Let me see if I've got it:

xsl:for-each should be thought of as all items in the selected sequence being
processed in parallel. Consequently, "breaking out" of the loop makes no
sense.

xsl:iterate should not be thought of that way.  xsl:iterate should be thought
of as iterating sequentially, from the first item to the last item.
Consequently, "breaking out" of the loop makes good sense.

To my way of thinking, streaming means that we start at the top and
sequentially make our way through the document (or break out if desired).
Given that, it seems like when doing streaming Best Practice is to use
xsl:iterate and not use xsl:for-each. Do you agree?

/Roger

-----Original Message-----
From: David Carlisle [mailto:davidc@xxxxxxxxx]
Sent: Thursday, August 29, 2013 9:23 AM
To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
Cc: Costello, Roger L.
Subject: Re: [xsl] [XSLT Streaming] Are xsl:for-each and xsl:iterate
equivalent?

On 29/08/2013 14:10, Costello, Roger L. wrote:
> I realize that xsl:iterate has some capabilities that xsl:for-each
> doesn't have, such as the ability to break out of the loop before
> processing the entire sequence.
>
> But leaving that aside, they are both ways of looping over a
> sequence of items, right?

It's best not to think of for-each in those terms (even though it can be
streamed if the select attribute xpath is streamable) as in general it
gives no guarantee on execution order at all (which is why it wouldn't
make sense to "break out" of the loop). It is best to think of it as
being a parallel region in which all the selected items are processed
(even if a given, or all, implementations actually process the items one
at a time)

David


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