Re: Variable: true or false

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Subject: Re: Variable: true or false
From: Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>
Date: Fri, 06 Apr 2001 16:52:09 +0100

Hi Tom:

This is very tricky.

Problem is, your declaration

<xsl:variable name="selectUser"/>

isn't as "empty" as it looks. Absent a select expression, the variable contains a result tree fragment. XSLT (11.1) says about this special data type that it "is treated equivalently to a node-set that contains just a single root node" (going on to qualify this considerably). That is, if you had the declaration

  <xsl:variable name="selectUser">
      <holla/>
   </xsl:variable>

the variable $selectUser would be bound to a result tree fragment with a structure containing two nodes, a root and a single child (an element named 'holla'). But yours contains just that single root.

Alas, when this is treated as a node-set containing a root for purposes of evaluating the boolean() function, this comes out as true().

If you'd said

 <xsl:variable name="selectUser" select="''"/>
 (setting the value to be the empty string), or

 <xsl:variable name="selectUser" select="false()"/>
 (a boolean false), or even

 <xsl:variable name="selectUser" select=""/>
 (the null expression evaluates to an empty node set),

...*then* you'd have gotten false as you expected.

This is only one reason result tree fragments are troublesome. Since they are also of questionable utility, rumor has it they may be invited to leave, disappearing from future versions of XSLT. Then you'll get an (empty) node set as you expected.

Cheers,
Wendell

At 09:02 PM 4/6/01, you wrote:

I do the transform on this XSL and get "true". I would have expected
"false".
Thought the boolean of an empty object would always be false.

Using Xerces 1.4 and Xalan 1.1

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0">
   <xsl:variable name="selectUser"/>
   <xsl:template match="/">
      <xsl:choose>
         <xsl:when test="$selectUser">
            true
         </xsl:when>
         <xsl:otherwise>
            false
         </xsl:otherwise>
      </xsl:choose>
   </xsl:template>
</xsl:stylesheet>

Tom Gilbert
tom.gilbert@xxxxxxxxxxxxx


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Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
Mulberry Technologies, Inc.                http://www.mulberrytech.com
17 West Jefferson Street                    Direct Phone: 301/315-9635
Suite 207                                          Phone: 301/315-9631
Rockville, MD  20850                                 Fax: 301/315-8285
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======================================================================

XSL-List info and archive: http://www.mulberrytech.com/xsl/xsl-list

Current Thread

Re: RE: Variable: true or false, (continued)
- Tom Gilbert - Fri, 6 Apr 2001 16:02:58 -0400 (EDT)
  - Wendell Piez - Fri, 6 Apr 2001 16:52:10 -0400 (EDT) <=
  - Jeni Tennison - Sat, 7 Apr 2001 04:04:13 -0400 (EDT)
- David_N_Bertoni - Sat, 7 Apr 2001 03:06:32 -0400 (EDT)
  - Michael Kay - Sat, 7 Apr 2001 07:31:41 -0400 (EDT)
- David_N_Bertoni - Sat, 7 Apr 2001 22:19:24 -0400 (EDT)

<- Previous	Index	Next ->
Variable: true or false, Tom Gilbert	Thread	Re: Variable: true or false, Jeni Tennison
Using XPath for node assignme, Andrew Von Dollen	Date	Re: Using XPath for node assi, Johannes Döbler
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