Re: [xsl] The identity transform and attributes

[Abel Braaksma <abel.online@xxxxxxxxx>]

Or this way of writing, which however makes overriding attribute through 
templates not an option:

<xsl:template match="node()">
   <xsl:copy>
       <xsl:copy-of select="@*" />
       <xsl:apply-templates select="node()"/>
   </xsl:copy>
</xsl:template>


But if speed is the discussion point here, I think that optimalisation 
is rather good. Meaning that your two versions (and possibly mine) do 
not cost any extra clock cycles, because the internal representation is 
(just about) equal anyway. But that's a terrain I know little about, 
perhaps Michael Kay can shed some light on that?

Btw, it is never possible to override the text() of an attribute. An 
attribute does not have children. I.e., the following would be nice to 
prevent the shallow copy to copy both the attribute and the text and 
then treat the text "child" of the attribute separately (and override 
special cases), but that's not gonna work:

<xsl:template match="@*">
    <xsl:attribute name="{name()}">
         <xsl:apply-templates select="text()" />
     </xsl:attribute>
</xsl:template>

<xsl:template match="@specialcase/text()">
    <xsl:text>other text</xsl:text>
</xsl:template>


I believe that on most processors the above will give you a compile time 
warning about child axis of attributes not selecting anything.

About your question whether "apply-templates has any effect on an 
attribute" I believe the answer is a definite no. And I am under the 
impression (but I cannot confirm from tests) that once an attribute is 
matched, any apply-templates to children of it are optimized away, as 
they have no effect anyway.

Cheers,

-- Abel Braaksma

Andrew Welch wrote:
> I'm wondering if the default identity transform should be this:
>
> <xsl:template match="@*|node()">
>     <xsl:copy>
>         <xsl:apply-templates select="@*|node()"/>
>     </xsl:copy>
> </xsl:template>
>
> Or this:
>
> <xsl:template match="node()">
>     <xsl:copy>
>         <xsl:apply-templates select="@*|node()"/>
>     </xsl:copy>
> </xsl:template>
>
> <xsl:template match="@*">
>     <xsl:copy/>
> </xsl:template>
>
> The former is nice and compact, but when the node is an attribute node
> does the apply-templates call have any effect - even if it's a few
> clock cycles wasted?  It's a pointless instruction at that point.  I
> guess it is too for non-element node()'s such as whitespace?
>
> Also, the shallow copy copies the entire attribute, so there is no
> opportunity to override the text() of the attribute.  The only way is
> to add a separate matching template for the attribute - the latter
> perhaps makes this a little clearer.
>
> A useful distinction or a waste of time? :)
>
> cheers