Subject: Re: [xsl] Only child test From: Wendell Piez <wapiez@xxxxxxxxxxxxxxx> Date: Mon, 14 Oct 2013 09:44:58 -0400 |
Hi (please forgive the belated post), There's also test="exists(../* except .)" Plus similar variations on the theme. I think this one translates even more directly into the requirement as expressed in natural language, while giving the maintainer a chance to think about exists() and 'except' if need be. (Yes, I know 'except' can be a little painful -- another reason to keep in practice with it.) What an optimizer will do or how it will compare to ".//*[2]" I can't say -- although I'm also trying to train myself not to care too much about microseconds except when they are adding up. :-) Cheers, Wendell Wendell Piez | http://www.wendellpiez.com XML | XSLT | electronic publishing Eat Your Vegetables _____oo_________o_o___ooooo____ooooooo_^ On Thu, Oct 10, 2013 at 8:22 PM, Peter West <lists@xxxxxxxxx> wrote: > It's an endemic problem, and it's multi-layered. Express this particular "atomic" problem more human-understandably, and the problem rises up a level. Computers lack any notion of intention; programmers (hopefully) express intention. The most experienced practitioner of a programming language can be flummoxed in trying to discern the intention of some piece of code. And again, that puzzlement is multi-layered. > > None of which is to diminish the vital importance of the principles Ken has expressed. > > Peter West > > "'...neither would they be convinced if someone should rise from the dead.'" > > On 11/10/2013, at 12:02 AM, G. Ken Holman <gkholman@xxxxxxxxxxxxxxxxxxxx> wrote: > >> At 2013-10-10 10:02 +0100, Michael Kay wrote: >>> On 10 Oct 2013, at 09:42, CbC Cb!CB5C CB;CB0CB2 CB!CB5CB4CB>CB2 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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