RE: Passing empty parameters discard parameters defaul

> 
> I am having problems with passing empty parameters (no 
> with-param specified) that discard default values of 
> parameters. When I am calling the template and passing no 
> value I want the template to use its default value.
> 
> Example:
> 
>   <xsl:template name="mytemplate">
>     <xsl:param name="p"/>

This is exactly the same as specifying

<xsl:param name="p" select="''"/>

that is: $p is given a value which is the zero-length string. You are then
supplying this value to the other template. The only way to get the second
template to use its default value for the parameter is to omit the
xsl:with-param from the call.

Michael Kay


>     <xsl:call-template name="mytemplate_impl">
>       <xsl:with-param name="p" select="$p"/>
>     </xsl:call-template>
>   </xsl:template>
>   
>   <xsl:template name="mytemplate_impl">
>     <xsl:param name="p">default p</xsl:param>
>     p = <xsl:value-of select="$p"/>
>   </xsl:template>
> 
> When calling:
>     <xsl:call-template name="mytemplate_impl"/>
> the result is:
> 	p = default p
> But when calling 
>     <xsl:call-template name="mytemplate"/>
> the result is:
> 	p =
> 
> what is wrong in my case, becase I did not supplied any value 
> to parameter $p so I want to see its default value. I know 
> that I can declare the same default value in template 
> "mytemplate" , but then I will have the same value in more 
> than one place and that's not good when I will need to change it.
> 
> Is there any workaround for my problem?
> 
> Thank you, 
> Michal
> 
> PS: If you want to have full pricture why I need this default 
> parameter mechanism, here it is:
> 
> I have hierarchy of importing stylesheets and I try to 
> simulate polymorphism for named templates via shadowing of 
> "interface" templates and by calling "implementation" templates.
> 
> library.xsl:
>   <!-- interface template -->
>   <xsl:template name="mytemplate">
>     <xsl:param name="p"/>
>     <xsl:call-template name="mytemplate_impl">
>       <xsl:with-param name="p" select="$p"/>
>     </xsl:call-template>
>   </xsl:template>
> 
>   <!-- implementation template -->
>   <xsl:template name="mytemplate_impl">
>     <xsl:param name="p">default p</xsl:param>
>     p = <xsl:value-of select="$p"/>
>   </xsl:template>
> 
> customized-library.xsl:
>   <xsl:import href="library.xsl"/>
> 
>   <!-- interface template -->
>   <xsl:template name="mytemplate">
>     <xsl:param name="p"/>
>     <b>
>       <xsl:call-template name="mytemplate_impl">
>         <xsl:with-param name="p" select="$p"/>
>       </xsl:call-template>
>     </b>
>   </xsl:template>
> 
> user-stylesheet.xsl:
> 
>   <xsl:include href="customized-library.xsl"/>
>   ...
>   <xsl:template match="/">
>     <xsl:call-template name="mytemplate"/>
>   </xsl:template>
> 
> user-input.xml:
> <?xml-stylesheet type="text/xsl" href="user-stylesheet.xsl"?>
> <root/>
> 
> required output:
>   <b>p = default p</b>
> 
> actual output:
>   <b>p = </b>
> 
> I hope the idea is ok, developer of user-stylesheet.xsl can 
> customize templates from library.xsl that he/she uses in 
> user-stylesheet.xsl. But I am having the problem with passing 
> empty parameter (no parameter) that discard default value in 
> original template.
> 
> -----------
> Michal Ďurdina
> ASSET Soft, a.s. / eBussiness Solutions
> Košická 56, 821 08 Bratislava SLOVAK REPUBLIC
> Phone: +421-2-50703-523
> Fax: +421-2-50703-444
> e-mail: michal.durdina@xxxxxxxxxxxx
> 
> http://www.assetsoft.sk 
> 
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