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    <blockquote> <p>a) Can I automatically get a value of boolean true|false directly from the string 'true|false' ? </p> <p>b) Is there an (xpath?) construct to map the boolean true|false to '*', '' ?</p> </blockquote> <p><strong>This is actually an XPath question</strong>.</p> <p><strong>I. XPath 1.0</strong></p> <p>There are more than one XPath expressions the evaluation of which produces the wanted result:</p> <pre><code>substring('*', 2 -(@flag = 'true')) </code></pre> <p>This also answers b) -- notice that the <em>strings</em> <code>'true'</code> and <code>'false'</code> aren't boolean values! The only two boolean values are <code>true()</code> and <code>false()</code> and they are not strings.</p> <p>In the above expression we use the fact that in XPath 1.0 if a boolean is in a context where a number is needed, it is automatically converted to number. By definition:</p> <p><code>number(true())</code> is <code>1</code></p> <p>and</p> <p><code>number(false())</code> is <code>0</code></p> <p>Thus the second argument of the call to <code>substring()</code> above:</p> <pre><code>2 - (@flag = 'true') </code></pre> <p>is evaluated as <code>1</code> when <code>@flag = 'true'</code> and to <code>2</code> otherwise.</p> <p><strong>A more general XPath 1.0 expression that produces the string <code>$s1</code> if <code>$val</code> is <code>"x"</code> and produces the string <code>$s2</code> if <code>$val</code> is <code>"y"</code></strong> :</p> <pre><code>concat(substring($s1, 1 div ($val = "x")), substring($s2, 1 div ($val = "y")) ) </code></pre> <p>This produces the string <code>$s1</code> when <code>$val = "x"</code>, the string <code>$s2</code> when <code>$val = "y"</code>, and the empty string -- if none of these two conditions holds.</p> <p>The above XPath 1.0 expression can be generalized to produce N different string results <code>$s1</code>, <code>$2</code>, ..., <code>$sN</code> exactly when <code>$val</code> is one of the values <code>$v1</code>, <code>$v2</code>, ..., <code>$vN</code> because the function <code>concat()</code> can have any number of arguments.</p> <hr> <p><strong>II. XPath 2.0 (XSLT 2.0)</strong></p> <pre><code>'*'[current()/@flag = 'true'] </code></pre> <p>And more generally, given 2*N atomic values <code>$s1</code>, <code>$s2</code>, ... <code>$sN</code> and <code>$v1</code>, <code>$v2</code>, ..., <code>$vN</code>, such that all <code>$vi</code> values are different, the result of evaluating this XPath 2.0 expression:</p> <pre><code> ($s1, $s2, ..., $sN)[index-of(($v1, $v2, ..., $vN), $v)] </code></pre> <p>is <code>$sK</code> exactly when <code>$v eq $vK</code>.</p>
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    1. COMany thanks for this - why '2-x' and not '1-x' though?
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    2. CO@monojohnny: Good question. The reason for '2-x' is to get 1 or 2. XPaths indexing is 1-based , not 0-based.
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    3. COah yes, I forgot XSL strings are 1-bound ! Cheers ! makes sense.
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