RE: [xsl] Avoiding multiple "apply-templates" by creating one variable for the clauses. Is it possible?

["Michael Kay" <mike@xxxxxxxxxxxx>]

> >       <xsl:apply-templates select="//blog
> >                            [not($AuthorId) or (author_id = $AuthorId)]
> >                            [not($CategoryId) or (category_id =
$CategoryId)]
> >                            "/>
> 
> I guess I'll finally drop in and add another suggestion since 
> I've been waiting for one of my XSLT students to bring it up 
> but I don't see any of them doing so.
> 
> If you are looking for compactness, I believe the above 
> expression can be reduced to the following in both XSLT 1.0 
> and XSLT 2.0:
> 
>        <xsl:apply-templates select="//blog
>                             [not($AuthorId != author_id)]
>                             [not($CategoryId != $CategoryId)]
>                             "/>
> 

I'm not convinced about this equivalence. If $AuthorId is "Mike", and
author_id is an empty sequence, then

 (a)  not($AuthorId) or (author_id = $AuthorId)  ==>  false

 (b)  not($AuthorId != author_id)  ==>  true

So if the optimizer does this conversion for you, it's wrong!

But it's probably safe if author_id will always be a singleton node-set.

Regards,

Michael Kay
http://www.saxonica.com/
http://twitter.com/michaelhkay