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RE: [xsl] how to call extension function for side-effect, portably?

Subject: RE: [xsl] how to call extension function for side-effect, portably?
From: "Michael Kay" <mike@xxxxxxxxxxxx>
Date: Wed, 19 Jan 2005 00:21:12 -0000

saxon:discard-document is deliberately designed to return the document being
discarded, so you can wrap it round a call of document(), or any other
reference to the document is actually being used. (It's effect isn't
immediate, it merely marks the document as being available for garbage
collection when no longer referenced).

In general, if you're not using the result of a function but still want it
called, then you should try to hoodwink the optimizer into thinking that you
are using it. If it's a Java method that returns void, call it as

<xsl:sequence select="my:call(xyz)"/>

or call it as

<xsl:if test="my:call(xyz) = -1"><a/></xsl:if>

when you know the result will never be -1.

Michael Kay

> -----Original Message-----
> From: Kevin Rodgers [mailto:kevin.rodgers@xxxxxxx] 
> Sent: 18 January 2005 20:46
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject: [xsl] how to call extension function for 
> side-effect, portably?
> What is the appropriate XSL instruction to call an extension for
> side-effect only?  Currently I've got this in my stylesheet:
>   <xsl:variable name="foo"
>      select="document('file:///tmp/foo.xml')"/>
>   <xsl:if test="function-available('saxon:discard-document')"
>      xmlns:saxon="http://saxon.sf.net/">
>     <xsl:variable name="dummy"
>        select="saxon:discard-document($foo)"
>        xmlns:saxon="http://saxon.sf.net/"/>
>   </xsl:if>
> Which not surprisingly generates a warning (from Saxon):
> Warning: at xsl:variable on line 11 of file:/tmp/foo.xsl:
>   A variable with no following sibling instructions has no effect
> -- 
> Kevin Rodgers

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