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Subject: Re: decorator / wrapper design pattern
From: Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>
Date: Fri, 18 Mar 2005 11:31:59 -0500
Hi Lucas,

I'm not sure whether this could rightly be said to map to the "decorator" pattern (maybe so), but it seems to me you may be looking for the idiom:

<xsl:template match="something">
  <xsl:call-template name="some-wrapper"/>
</xsl:template>

<xsl:template name="some-wrapper">
  <xsl:param name="contents">
    <xsl:apply-templates/>
  </xsl:param>
  <wrapper>
    <xsl:copy-of select="$contents"/>
  </wrapper>
</xsl:template>

this allows you also to do things like

<xsl:template match="something-else">
  <xsl:call-template name="some-wrapper">
    <xsl:with-param select="contents">
      <xsl:call-template name="some-other-wrapper"/>
    </xsl:with-param>
  </xsl:call-template>
</xsl:template>

or even

<xsl:template match="another-something-else">
  <xsl:call-template name="some-wrapper">
    <xsl:with-param select="contents">
      <xsl:text>Wrap me!</xsl:text>
    </xsl:with-param>
  </xsl:call-template>
  <xsl:apply-templates/>
</xsl:template>

That is, the "wrapper" (or decorator) template can wrap anything you pass it.

A "thick" solution to a nasty problem (map a set of attributes to a set of wrappers) using this idiom (although by matching templates, not calling them by name) appears at

But I should also caution you that it isn't very common to have to do this; lighter-weight solutions are usually possible. Also, as Jay says, the requirements this addresses are often better answered by pushing the problem into the next layer up, for example into a CSS stylesheet to be applied to HTML output.

Enjoy!
Wendell


At 08:37 AM 3/18/2005, you wrote:
Hi,

I'm using XSL version 1.0 and am trying to use the decorator design
pattern, but can't get it to work in XSL.
Here is what I try to achieve:
Different types of elements all need to be surrounded by the same text.
For example:

I've XML:
<base>
  <section>
     <title>the title</title>
     <paragraph>some text</paragraph>
     <paragraph>more text</paragraph>
  </section>
  <section>
     <title>the title</title>
     <paragraph>other text</paragraph>
     <paragraph>more other text</paragraph>
     <paragraph>and more text</paragraph>
  </section>
</base>

Now I want all text in titles and in paragraphs to be italic and in
titles also to be bold.
My first thought was to use call-template like this:
<xsl:template match="title">
  <xsl:call-template name="bold">
    <xsl:call-template name="italic">
       <xsl:value-of select="."/>
    </xsl:call-template>
  </xsl:call-template>
</xsl:template>

But this is not the way to do this.
I cannot however figure out or find the solution. The decoration that
must be applied is much more complicated than bold or italic, but that
is besides the point, I think.
Here is my second try, but here is the problem that I cannot nest
decorators, so bold and italic is not possible on the same element:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0">

<xsl:template match="/">
  <xsl:call-template name="body"/>
</xsl:template>

<xsl:template match="section">
  <xsl:apply-templates />
  <br/>
</xsl:template>

<xsl:template match="title">
  <xsl:call-template name="bold" />
  <br/>
</xsl:template>

<xsl:template match="paragraph">
  <xsl:call-template name="italic" />
</xsl:template>

<xsl:template name="bold">
  <b>
     <xsl:apply-templates/>
  </b>
</xsl:template>

<xsl:template name="italic">
  <i>
     <xsl:apply-templates/>
  </i>
</xsl:template>

<xsl:template name="body">
  <html>
    <body>
      <xsl:apply-templates />
    </body>
  </html>
</xsl:template>

</xsl:stylesheet>


Can anybody give me a pointer?

Thanks in advance

Lucas 


======================================================================
Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
Mulberry Technologies, Inc.                http://www.mulberrytech.com
17 West Jefferson Street                    Direct Phone: 301/315-9635
Suite 207                                          Phone: 301/315-9631
Rockville, MD  20850                                 Fax: 301/315-8285
----------------------------------------------------------------------
  Mulberry Technologies: A Consultancy Specializing in SGML and XML
======================================================================

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