Re: [xsl] XPath that returns nothing

[David Carlisle <davidc@xxxxxxxxx>]

On 28/09/2011 11:34, Andrew Welch wrote:
> On 28 September 2011 11:25, David Carlisle<davidc@xxxxxxxxx>  wrote:
> > On 28/09/2011 11:18, Andrew Welch wrote:
> > > ...but... only if you don't specify the as attribute -
> >
> > ah yes, although actually we have mixed experience of using as=, tend to use
> > it less and less (despite MK's periodic reminders of the potential
> > efficiency from optimisations that the extra information
> > that the xslt engine can make given the information).
>
> Ah that's interesting / controversial :) Do you have an example of
> where you were using it but decided to remove it?

our usual situation is we're running the same stylesheet over a couple 
of thousand input documents. With the way we are currently pipelining 
these transformations, if you have a function that expects a single 
element and you go
xsl:param name="x" as="element()"
then if one of the input documents is bad the error percolates up to the 
top level and not only that document fails to produce but the entire run 
is aborted.

if on the other hand you don't use as="element()" but instead you accept 
anything but have
<xsl:if test="exists($x[2]) or not($x/self::*)">
  <xsl:message select='excuse me, I think parameter x might be wrong'"/>
</xsl:if>

then the run proceeds to the end but problems get logged more gracefully.

It may be that by using a different pipelining strategy each document 
could be isolated but I think (until there is a try/catch facility 
within xslt) errors reported by as= attributes will be fatal errors and 
so stop at the very least that document.

David

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