Re: [xsl] how to assign a NULL to a variable?

[Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>]

Justin,

String operations can also be performed on result tree fragments, 
which are implicitly cast to strings in such cases, so string($rtf) 
will return the empty string "" if there is "nothing" in the RTF.

(By "nothing" I mean "something signified by the English word 
'nothing'", not the literal word or string "nothing". These are the 
hazards in talking about nulls. In point of fact string($rtf) will 
also be "" if it contains only empty elements, which can complicate things.)

I don't run across NULL much in my work; for me, Boolean false(), 
empty sequences or node-sets or strings generally suffice. So the 
question I have for the OP is "what do you mean by 'NULL'?" Something 
that tests as "null" (it has no stated value) and something that 
represents nullity in the output might be two different things, as you imply.

In any case, it's sometimes useful even in XSLT 1.0 to do something like:

<xsl:variable name="result">
  <xsl:apply-templates/>
</xsl:variable>
<xsl:if test="normalize-space($result)">...</xsl:if>

though unfortunately (and perhaps counter-intuitively), $result by 
itself (that is, not cast explicitly by string() or coerced by 
normalize-space()) will be cast to Boolean true() even if there is no 
result from the apply-templates, by virtue of the RTF having a root.

Cheers,
Wendell

At 11:50 AM 7/26/2007, you wrote:
> >> In XSLT 1.0 you have 4 datatypes: number, boolean, string and nodeset.
> >
> >actually there is another, and that is the type that will be returned in
> >this case (with an xsl:variable with eleemnt content).
> >result tree fragment.
> >
>
> Well, yes.  Forgot about that in 1.0 but how would the OP test for a result
> tree fragment
> for the purposes of signifying "nil" or "null" without incurring a runtime
> error, given that the operations
> permitted on a result tree fragment are a subset of those permitted on a
> node-set?
>
> Justin Johansson
>
> *** A horse with no name is called Lambda ***


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Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
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