Re: [xsl] [xslt 2.0] Difference betwen functions and templates

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

On 7/19/07, Abel Braaksma (online) <abel.online@xxxxxxxxx> wrote:
> I think I believed the wrong term, I meant method overloading
> instead of polymorphism. I don't agree with your statement that
> single polymorphism is what is offered by XSLT. I

Not out-of-the box, but you can re-create it.  "Polymorphism"  is
still a suitable term imho.


> POLYMORPHISM
> If such a thing would exist it might look something like this:
>
> <xsl:module name="mod:cat" implements="animal">
>    <xsl:function name="talk">Meow!</xsl:function>
>    <xsl:function name="name">Cat</xsl:function>
> </xsl:module>
>
> <xsl:module name="mod:dog" implements="animal">
>    <xsl:function name="fu:talk">Bark!</xsl:function>
>    <xsl:function name="fu:name">Cat</xsl:function>
> </xsl:module>
>
> <xsl:module name="mod:animal">
>    <xsl:function name="fu:talk" deferred="yes">
>    <xsl:function name="fu:name" deferred="yes">
>    <xsl:function name="fu:say-name">
>       <xsl:sequence select="fu:talk(), ' I am a ', fu:name()" />
>    <xsl:function>
> </xsl:module>
>
> <!-- suppose that a module can be called like a xpath axis, then -->
> <xsl:template match="/">
>    <xsl:sequence select="'mod:dog:', mod:dog::say-name()" />
>    <xsl:sequence select="'mod:cat:', mod:cat::say-name()" />
> </xsl:template>
>
> <!-- output will then be -->
> mod:dog: Bark! I am a dog
> mod:cat: Meow! I am a cat

Not quite - that should really be "mod:animal::say-name()" called
twice to be polymorphism - you're calling the "concrete" method there
rather than the abstract.

So to recreate your example using named templates and import precedence:

Animal.xslt
<xsl:template name="sayName">
	<xsl:value-of select="$name"/>
</xsl:template>

And then Dog.xslt:
<xsl:import href="animal.xslt"/>

<xsl:variable name="name" select="'Dog'"/>
	
<xsl:template match="/">
	<xsl:call-template name="sayName"/>
</xsl:template>

And the equivalent Cat.xslt would just have the different variable:
<xsl:variable name="name" select="'Cat'"/>


So why is this polymorphism?  Because the common Animal.xslt will use
the $name variable depending on how the transform was constructed.
You call "sayName" in the Animal stylesheet and that uses the $name
variable in the Dog/Cat stylesheet.

The Animal stylesheet is kind-of abstract in that it won't run on it's
own because it lacks a declaration for $name.

Perhaps in the future if "compiled stylesheet modules" become a
reality then abstract and final modifiers for templates and functions
will be included too.

http://www.biglist.com/lists/xsl-list/archives/200506/msg00429.html

--
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