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Re: [xsl] Re: Benefits of xsl.sequence

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> but is the benefits something we can measure in any meaningful sense?


In some cases xsl:sequence may or may not be more efficient than using
value-of, but that's not really the point. In most cases if you need to
return a sequence from a template or function, xsl:sequence is the only
option, if no other instruction can generate the same result, then
efficiency doesn't really come into it.


For example consider a function that concatenates two sequences which
you don't really need to write as it is the comma operator

<xsl:function name="f:concat">
 <xsl:param name="a"/>
 <xsl:param name="a"/>
 <xsl:sequence select="$a,$b"/>
</xsl:function>

so 

f:concat( (1,2,3) , (4,5,6) )

is 

(1,2,3,4,5,6)

If you replaced xsl:sequence by xsl:value-of then the result would not
be a sequence of six items, but instead a sequence of one item, a text
node with string value "1 2 3 4 5 6" which isn't the same thing at all.

For sequenes of attomic values as here, you could use xsl:copy-of which
which would be identical to xsl:sequence, but for sequences of nodes
copy-of implies a copy which is (conceptually) a copy.

Actually the efficicency quextion may be hard to answer as systems may
go to some lengths to avoid actually copying nodes, so copy-of may be as
efficient as sequence of, but the behaviour is different.

Condider an identity function

<xsl:finction name="f:ident">
 <xsl:param name="x"/>
 <xsl:sequence select="$x"/>
</xsl:function>

f:ident($node) is the same node as $node, it has the same parent (if
$node has a $parent), siblings, etc


f:ident($node)/following-sibling::* is the same as $node/following-sibling::*



If you replace xsl:sequence by xsl:value-of in the above then
xsl:ident($node) would  be a textnode with the string value of $node,
and if you replace xsl:sequence by xsl:copy-of then $ident($node) would
_look_ like $node but it would be a new node, with no parents or
siblings.

David

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