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RE: [xsl] xsl:sequence

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> If a variable value is a 
> reference rather than a copy what advantages does that provide?

Firstly, it saves the cost of doing a copy (actually Saxon makes a virtual
copy, but it still has a cost). Secondly it means you can still navigate
from the node to its original parent, ancestors, and siblings. Thirdly it
means you can do identity-related operations such as union and "<<".

Michael Kay
http://www.saxonica.com/


> 
> 
> > > Does <xsl:sequence select="@price"/> not assign an 
> attribute node to 
> > > the variable $prices? If so surely this is wasteful?
> >
> >it references an _existing_ attribute node, but this is 
> coerced to an 
> >atomic xsl:double value because of the as attribute which 
> specifies the 
> >variable holds a sequence of doubles. I'm not clear where 
> you see the 
> >waste.
> 
> I was thinking that an attribute node contains a text node. 
> Reading up on it an attribute node seems to *be* both the 
> attribute name and its value. When it is co-erced to an 
> atomic xs:double value it somehow loses the attribute name 
> part and just takes on the value - this is what I was 
> referring to as waste.
> 
> 
> >From: David Carlisle <davidc@xxxxxxxxx>
> >Reply-To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> >To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> >Subject: Re: [xsl] xsl:sequence
> >Date: Mon, 7 Aug 2006 11:20:55 +0100
> >
> > > Apologies for these seemingly random questions but I have read 
> > > numerous resources and am still struggling to understand why 
> > > xsl:sequence is so important.
> >
> >It's important, especially in variable and function 
> definitions, as it 
> >allows the return of _existing_ nodes rather than copies of nodes.
> >
> >
> > > <xsl:sequence select="." /> is constructing new nodes in 
> the output 
> > > that
> >is,
> > > in effect, a copy-of the context node.
> >
> >No, it selects the current node. (unlike <xsl:copy-of which would 
> >construct a copy). If the xsl:sequence is being used to generate an 
> >output result tree, then the difference is slight, as there is an 
> >implied copying anyway in that construction, but if the current 
> >template is being used to construct the value of a 
> variable.there is a 
> >big difference. In one case the variable will have a 
> reference to teh 
> >current node, and in teh other it will have a reference to a copy.
> >
> > > 2. I also understand sequence allows you to construct a 
> sequence of 
> > > different datatypes in one expression,
> > >
> > > What, then, is the point of the concat function in XSLT 
> 2? ie could
> >
> >concat serves a completely different purpose, it 
> concatenates strings, 
> >producing a single string.
> >
> > > What, then, is the point of the concat function in XSLT 
> 2? ie could
> >
> > > <xsl:sequence select="concat(meta/brand/text(), ' | ', 
> > > genre/text())"/>
> >
> > > be rewritten:
> >
> > > <xsl:sequence select="meta/brand/text(), ' | ', genre/text()"/>
> >
> >The first one makes a sequence of one item, a string.
> >
> >The second one makes a sequence of three items, a text node, 
> a string 
> >and a text node
> >
> >Compare
> >
> ><xsl:value-of separator=",">
> >   <xsl:sequence select="concat(meta/brand/text(), ' | ',
> >   genre/text())"/>
> ></xsl:value-of
> >
> ><xsl:value-of separator=",">
> >   <xsl:sequence select="meta/brand/text(), ' | ',
> >   genre/text()"/>
> ></xsl:value-of
> >
> >
> >
> > > Does <xsl:sequence select="@price"/> not assign an 
> attribute node to 
> > > the variable $prices? If so surely this is wasteful?
> >
> >it references an _existing_ attribute node, but this is 
> coerced to an 
> >atomic xsl:double value because of the as attribute which 
> specifies the 
> >variable holds a sequence of doubles. I'm not clear where 
> you see the 
> >waste.
> >
> >David
> >
> 
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