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RE: [xsl] XPath/XSLT 2.0: What is the most efficient way to find if a sequence is empty?


Subject: RE: [xsl] XPath/XSLT 2.0: What is the most efficient way to find if a sequence is empty?
From: "Michael Kay" <mhk@xxxxxxxxx>
Date: Sun, 5 Oct 2003 15:46:18 +0100

There are two complementary functions empty($seq) and exists($seq).

I would expect any decent optimizer to generate exactly the same code
for these as for count($x)=0 - but I guess there are processors out
there that don't have decent optimizers.

Michael Kay

> -----Original Message-----
> From: owner-xsl-list@xxxxxxxxxxxxxxxxxxxxxx 
> [mailto:owner-xsl-list@xxxxxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Dimitre Novatchev
> Sent: 04 October 2003 22:00
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject: [xsl] XPath/XSLT 2.0: What is the most efficient way 
> to find if a sequence is empty?
> 
> 
> In XSLT/XPath 1.0 one would use:
> 
>   not($node-set)
> 
> to find if $node-set is the empty node-set.
> 
> However, the same test on a sequence in XPath 2.0:
> 
>   not($seq)
> 
> may return 'true' for a non-empty sequence -- e.g. for:
>    ( false() )
> 
> or for
> 
>        (0)
> 
> My question: Is there a more efficient test for an empty sequence than
> 
>   count($seq) = 0
> 
> 
> 
> 
> =====
> Cheers,
> 
> Dimitre Novatchev.
> http://fxsl.sourceforge.net/ -- the home of FXSL
> 
> 
> 
> 
>  XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list
> 


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