Hi Folks,
Here is my (very simple) XML document:
<Document>Hello, world</Document>
My XSLT program contains a xsl:value-of with a simple XPath expression:
<xsl:template match="/">
<xsl:value-of select="Document/foo eq 'abc'"/>
</xsl:template>
In the XPath expression I mistakenly referenced an element -- foo -- that does
not exist.
I ran the XSLT program on the XML document. No error was generated.
My colleague argues that such behavior is bad language design:
---------------------------------------------------
Languages which define such mistakes to just return "empty" node lists or
false, or such are not helping anybody. They just turn author mistakes into
silent, hard-to-detect behaviors. In my view this is a major mistake in the
XPath language.
All path expressions should be strongly, statically type-correct, so
Document/foo has to be a possible path. But if element foo is optional, then
any given instance may not have element foo and so a path like Document/foo can
be type correct, but meaningless for a particular data document. One can
explicitly test, e.g.,
if ( exists(Document/foo) ) then (Document/foo eq 'abc') else....
If you just use the expression without this test, and node foo doesn't exist,
then it should cause a failure.
---------------------------------------------------
Do you agree with my colleague's assessment? Is this behavior in XPath an
indication of bad language design?
/Roger
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