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Re: [xsl] Only child test


Subject: Re: [xsl] Only child test
From: "G. Ken Holman" <gkholman@xxxxxxxxxxxxxxxxxxxx>
Date: Thu, 10 Oct 2013 10:02:18 -0400

At 2013-10-10 10:02 +0100, Michael Kay wrote:
On 10 Oct 2013, at 09:42, PQQP5QP;P0P2 P!P5P4P>P2 wrote:

> can be test="../*[2]" faster?

A processor with a decent optimizer (e.g. Saxon) will do that rewrite for
you.

What is nice about this optimization is that it
leaves decisions about execution speed up to the
processor and not to the stylesheet writer.

From a maintenance perspective, what you are
trying to convey is a test of the number of siblings.  I think saying:

test="count(../*)>1"

... tells the incoming stylesheet maintainer the
essence of what is being tested, perhaps helping
them understand why the test is being done.  If
the maintainer comes into some code and sees:

test="../*[2]"

... they might be asking themselves "what is so
important about the second child?".  It might not
be their first thought that "is the current element without any siblings?".

Of course this might be obvious in this
particular situation to Karl and it doesn't
matter for his question, but I often will write
expressions trying to express the essence of the
reason for the expression, rather than quizzing
myself making a contest to find the most compact
or the fastest running equivalent expression.

Pleasing myself on my (self-perceived) prowess is
less important than writing code that isn't going
to confuse someone being handed my stylesheet for
maintenance when I'm not around.  I'm a
second-generation programmer and I well remember
such countenance from my father who, in his
position writing banking software on mainframes,
played both roles of having to maintain years-old
code and writing new code that was guaranteed to
be maintained by others years later.  One
conversation in particular was in 1994 when he
was modifying decades-old code that was not Y2K
aware handling 5-year term deposits.

Granted, my customers are in publishing and even
with some of the tomes they work on the
transformations happen infrequently enough that I
can rely on the skill of the engine writer to
make me look good at execution time.  It is my
responsibility to make me look good at maintenance time.

I hope this helps.

. . . . . . . . Ken


-- Public XSLT, XSL-FO, UBL & code list classes: Melbourne, AU May 2014 | Contact us for world-wide XML consulting and instructor-led training | Free 5-hour lecture: http://www.CraneSoftwrights.com/links/udemy.htm | Crane Softwrights Ltd. http://www.CraneSoftwrights.com/s/ | G. Ken Holman mailto:gkholman@xxxxxxxxxxxxxxxxxxxx | Google+ profile: https://plus.google.com/116832879756988317389/about | Legal business disclaimers: http://www.CraneSoftwrights.com/legal |


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