Re: [xsl] null call of document function

[Steve <subsume@xxxxxxxxx>]

Ok, thanks anywho.

Could you elaborate on the phrase "optimize away"? I understood it all
up until there.

-Steve

On 4/8/07, Michael Kay <mike@xxxxxxxxxxxx> wrote:
> Sorry, but advising on application design is much harder than advising on
> coding or debugging, and I really don't like doing it without knowing a lot
> more than this about your requirements and constraints. And it then becomes
> a consultancy assignment rather than a simple question+answer on a forum.
>
> It's easy to spot when someone is doing things the wrong way, it's sometimes
> much harder to identify the right way.
>
> Michael Kay
> http://www.saxonica.com/
>
>
> > -----Original Message-----
> > From: Steve [mailto:subsume@xxxxxxxxx]
> > Sent: 08 April 2007 01:47
> > To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> > Subject: Re: [xsl] null call of document function
> >
> > Maybe you could give me some additional guidance? My
> > situation is this:
> >
> > I have a sql table 'alerts' which contains system messages to
> > be delivered to the user.
> >
> > A call to my xsl template "getAlerts" calls a script which
> > serves these alerts up as XML and then clears them from the table.
> >
> > In some cases I want a file my user is viewing to generate an alert.
> > My idea was to use the document function to insert the alert,
> > and then later in the script it would be available for the
> > getAlerts template.
> >
> > Are you suggesting it would be wiser to insert this Alert in
> > my processing script pre-transform? Some other suggestion?
> >
> > -Steve
> >
> > On 4/7/07, Michael Kay <mike@xxxxxxxxxxxx> wrote:
> > > > What if I want to make a call to the document() function
> > but I don't
> > > > expect any value?
> > >
> > > That presumably means you expect the call to have side-effects.
> > >
> > > A call on the document function is analagous to an HTTP GET
> > request,
> > > and it's considered bad form for GET requests to have side effects:
> > >
> > > http://www.w3.org/2001/tag/doc/whenToUseGet.html
> > >
> > > At the XSLT level, calling document() and expecting
> > side-effects has
> > > all the problems associated with extensions functions that
> > have side
> > > effects, notably that the call is liable to be optimized
> > away if the
> > > result isn't used. In fact it's worse than extension
> > functions, because:
> > >
> > > (a) with extension functions, the optimizer might if you're
> > lucky take
> > > into account the possibility that the call has
> > side-effects; with the
> > > document() function this is unlikely
> > >
> > > (b) the semantics of the document() function essentially
> > say that if
> > > you make the same call twice with the same URI, it only
> > gets executed once.
> > >
> > > In short - don't do it.
> > >
> > > Michael Kay
> > > http://www.saxonica.com/