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[xsl] Using an empty xsl:for-each statement to "touch" elements


Subject: [xsl] Using an empty xsl:for-each statement to "touch" elements
From: "Costello, Roger L." <costello@xxxxxxxxx>
Date: Thu, 12 Dec 2013 10:40:40 +0000

Hi Folks,

Suppose you want to add together all the costs in this purchase order:

<purchase-order>
    <item>
        <cost>10</cost>
    </item>
    <item>
        <cost>20</cost>
    </item>
    <item>
        <cost>19</cost>
    </item>
    <item>
        <cost>25</cost>
    </item>
    <item>
        <cost>17</cost>
    </item>
</purchase-order>

The new XSLT 3.0 accumulator can be used. The accumulator is updated each time
a <cost> element is "touched". To "touch" each <cost> element I have this
empty loop:

<xsl:for-each select="item">
    <xsl:for-each select="cost"/>
</xsl:for-each>

That inner loop doesn't need any statements because its sole purpose is merely
to "touch" the cost element, and thereby trigger the accumulator to be
updated.

Here is the XSLT program with the accumulator:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                         xmlns:xs="http://www.w3.org/2001/XMLSchema"
                         exclude-result-prefixes="#all"
                         version="3.0">

    <xsl:output method="xml" />

    <xsl:accumulator name="f:item-cost"
                post-descent="f:total-item-cost"
                as="xs:integer"
                initial-value="0">
        <xsl:accumulator-rule match="cost" new-value="$value +
xs:integer(.)"/>
    </xsl:accumulator>

    <xsl:template match="purchase-order">
        <Total-Cost>
            <xsl:for-each select="item">
                <xsl:for-each select="cost"/>
            </xsl:for-each>
            <xsl:value-of select="f:total-item-cost()" />
        </Total-Cost>
    </xsl:template>

</xsl:stylesheet>

I realize that this problem could be solved in other ways, but I wanted to
show how it could be solved using an accumulator. And that invariably led me
to an empty xsl:for-each statement.

Is there a better way to "touch" an element than using an empty xsl:for-each
statement?

/Roger


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