Re: [xsl] Optimisation -- premature?

["Andrew Welch" <andrew.j.welch@xxxxxxxxx>]

On 2/11/07, John Horner <Horner.John@xxxxxxxxxx> wrote:
> I have a transformation which sometimes, depending on circumstances,
> creates bunch of variables used in an external function.
>
> Let's say that logic is like this:
>
> <xsl:if test="a_certain_flag_is_set">
>    <xsl:variable name="foo" select="foo"/>
>    <xsl:variable name="bar" select="bar"/>
>    <xsl:variable name="baz" select="baz"/>
>    <xsl:value-of select="namespace:function($foo,$bar,$baz)"/>
> </xsl:if>
>
> That's OK except that elsewhere in the stylesheet, if a different and
> mutually exclusive flag is set, I need to create exactly the same
> variables
>
> <xsl:if test="a_different_flag_is_set">
>    <xsl:variable name="foo" select="foo"/>
>    <xsl:variable name="bar" select="bar"/>
>    <xsl:variable name="baz" select="baz"/>
>    <xsl:value-of select="namespace:function($foo,$bar,$baz)"/>
> </xsl:if>
>
> I want to be more efficient about this, and would rather do this at the
> top of the stylesheet
>
> <xsl:if test="a_certain_flag_is_set
>               or
>               a_different_flag_is_set">
>    <xsl:variable name="foo" select="foo"/>
>    <xsl:variable name="bar"select="bar"/>
>    <xsl:variable name="baz" select="baz"/>
> </xsl:if>
>
> That is, create them once, if they're going to be needed by either
> function later in the processing. Because of the way scope works in XSL,
> I can't do this, can I? So, which of the two less efficient methods is
> best -- create them every time the process runs, although I may not need
> them, or duplicate their creation locally in the separate if-elements?
>
> It's not a problem as such, the process works just fine, but it's
> bugging me a little that I can't do it the "right" way.

It's a bit hard to say going on the samples you've provided, but some
suggestions are:

- Separate out the duplicate code into named templates or functions
(in 2.0).  Usually named templates are best when element creation is
needed, functions are best for computing values.

- If you have distinct choose/when/otherwise blocks then separate them
out into specific stylesheets that import a common stylesheet.

- Define the common variables "higher up" and use tunneling to get
them to the templates where they're used (again a 2.0 feature).

cheers
andrew