There's good news, and bad news.
The good news: The dfdl:newVariableInstance is the way this is supposed to work.
It creates a "stack allocated" variable. The variable and its type must be
declared at top level, then entering a scope having newVariableInstance
referencing that var creates a local one which is temporary, until the
parser/unparser leaves that scope.
The bad news: Alas.... Daffodil has not yet implemented newVariableInstance.
The good news: One can always achieve (for parsing anyway) the same thing by an
element having dfdl:inputValueCalc.
So below, instead of your
<xsl:variable name="Hidden_color_number"
select="../Hidden_color_number"/>
write
<xs:element name="HCN" type="xs:int"
dfdl:inputValueCalc='{ ../Hidden_color_number }' />
Instead of a variable you get an element, in this case "HCN", with a known and
fixed relative path, which is defined in terms of the expression which contains
the varying relative path that you are trying to keep out of your expression.
The existence of this work-around is one of the reasons we haven't gotten
around to dfdl:newVariableInstance as of yet.
This is one of the softer areas of the DFDL spec. This workaround works, but
only for parsing, since inputValueCalc elements aren't evaluated when
unparsing. So really we do need newVariableInstance to work; however, there are
shortcoming there as well having to do with array instances.
________________________________
From: Costello, Roger L. <[email protected]>
Sent: Monday, November 5, 2018 11:44 AM
To: [email protected]
Subject: Can I create a local variable in DFDL?
Hello DFDL community!
I want to create a local variable; is that possible in DFDL?
For example, I would like to create a variable to hold the value of a hidden
element and then use that variable in an inputValueCalc expression. Below I
show the idea: I create a variable named Hidden_color_number and then use that
variable in the inputValueCalc expression. I show creating an XSLT variable,
which is obviously not correct. Is there a way to do this in DFDL? /Roger
<xs:element name="enum-test">
<xs:complexType>
<xs:sequence>
<xs:sequence dfdl:hiddenGroupRef="hidden_Color_Group" />
<xsl:variable name="Hidden_color_number"
select="../Hidden_color_number"/>
<xs:element name='color' type='xs:string' dfdl:inputValueCalc="{
doc('Colors.xml')//row[number eq
xs:string($Hidden_color_number)]/symbol}" />
</xs:sequence>
</xs:complexType>
</xs:element>
