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Hi Folks, I think special case code is evil.
What properties must a programming language possess to enable programmers to reduce (or eliminate) the need for writing special case code? This might be an interesting research project for a
graduate student. Michael Kay gave a terrific example of avoiding special case code. He said this on the xsl-list: --------------------------------------------------------------- In XSLT 1.0 you often see code that does <xsl:for-each select="item"> <xsl:value-of select="."/> <xsl:if test="position() != last()"> <xsl:text>, </xsl:text> </xsl:if> </xsl:for-each> That's special case code to handle the last item in a list. In 2.0 we introduced the separator attribute, so this becomes <xsl:value-of select="item" separator=", "/> So yes, we made a language design change to reduce your need to write special-case code. --------------------------------------------------------------- That is just a portion of Michael’s message. I recommend reading his entire message, it is great: https://www.biglist.com/lists/lists.mulberrytech.com/xsl-list/archives/202106/msg00090.html
Last week I was grappling with a problem that seemed to require special case code but then Mukul Gandhi showed me a small tweak which resulted eliminating the need for special case code. Here
is a recap of that discussion: ---------------------------------------------------------------
I created the following XPath expression to fetch the <Row> element where Cell[1]/Data equals $element and Cell[2]/Data equals $parent. $document/Row[Cell[1]/Data eq $element][Cell[2]/Data eq $parent] However, when $parent is empty, the XPath expression fails. I was all set to write special case code: <xsl:if test="empty(Cell[2]/Data)"> do something </xsl:if> Bad, bad, bad. But then Mukul showed me an XPath expression that works correctly -- whether $parent is empty or not -- without any special case code: $document/Row[Cell[1]/Data eq $element][Cell[2]/string(Data) eq $parent] Just add string(…) around Data. Awesome! --------------------------------------------------------------- A few days ago I was writing some XSLT to show, for each element in an XML document, its name, the name of its parent, the name of its grandparent, and the name of its great-grandparent: <xsl:template match="*"> <row> <element><xsl:value-of select="name(.)"/></element> <parent-element><xsl:value-of select="name(..)"/></parent-element> <grandparent-element><xsl:value-of select="name(../..)"/></grandparent-element> <great-grandparent-element><xsl:value-of select="name(../../..)"/></great-grandparent-element> </row> <xsl:apply-templates select="*" /> </xsl:template> Obviously as the XSLT traverses through an XML document some elements don't have a great-grandparent or a grandparent or even a parent. But I didn't need to write special case code to check those conditions. That is terrific! To recap:
I welcome your thoughts and comments. /Roger |