Re: [qvto-dev] Bad Examples in 8.1.10

[Christopher Gerking <christopher.gerking@xxxxxxxxxxxxxxxx>]

Hi

 

 

Example 2:

 

I see no reason for premature return, at least not in this example. The resolveIn looks for an existing package which has been mapped from another class with the same package name. In case such a package is found, the result becomes non-null and the implicit instantiation section will not create a new package. There is no need to “avoid creating more than two packages having the same name” because the init section already ensures that package names are unique. And why “two”, is it a careless mistake?

 

The only reason for a premature return could be that the “name := self.packageName” initialization reexecutes unnecessarily. However there is no harm, and other ways exist to avoid that.

 

In Eclipse QVTo the init section can be rewritten more concisely as

 

result := resolveoneIn(JClass::jclass2jpackage, p : JPackage | self.packageName = p.name);

 

So yes, there are optional predicates for the target, but I also don’t understand why there is a “true” predicate.

The following is even more concise and should maybe make it to the specification:

 

result := resolveoneIn(jclass2jpackage, p | self.packageName = p.name);

 

The package name should be enough to select the resolved mapping, no need for the JCLass:: prefix. Also the p is already known as JPackage, so there should be no need for the additional : JPackage type indication.

 

 

Example 4:

 

The init section of the second mapping must be rewritten in order to update the correct Java interface. Therefore the resolveIn requires self as source:

 

mapping UML::Class::transformClassInheritance() : JAVA::Interface {

       init{

              result := self.resolveoneIn(UML::Class::transformClass);

       }

      

       base := self.superClass.resolveIn(UML::Class::transformClass);

}

 

 

Regards

Christopher

 

 

Von: qvto-dev-bounces@xxxxxxxxxxx [mailto:qvto-dev-bounces@xxxxxxxxxxx] Im Auftrag von Ed Willink
Gesendet: Sonntag, 4. Oktober 2015 14:07
An: QVTOML developer mailing list <qvto-dev@xxxxxxxxxxx>
Betreff: [qvto-dev] Bad Examples in 8.1.10

 

Hi

In Issue 15376 http://solitaire.omg.org/browse/QVT13-16, I complain that the examples in 8.1.10 are problematic.

The second example contains

"if result then return;"

which has a non-boolean condition _expression_ and a missing endif.

In the first example, it is not clear that the revisit adds rather than overwrites.

In the third and fourth examples it is not clear why the second pass reuses the context for the first rather than creates new objects.

5 years later this comes back to haunt me. With a slightly better understanding of QVTo, my complaints seem rather understated, the examples are quite terrible.

The attached ZIP file contains a project with launch configurations that represent my best attempt at making the examples work.

----

I cannot get the second example to work:

transformation JClass2JPackage(inout javamodel:JAVA);
main () { javamodel->objectsOfType(JClass)->jclass2jpackage();}
mapping Class::jclass2jpackage() : JPackage () {
init {
result := resolveIn(jclass2jpackage,true)
->select(p|self.package=p.name)->first();
if result then return;
}
name := self.package;
}

when changed to (JClass2JPackage.qvto):

modeltype JAVA uses 'http://www.omg.org/qvt/examples/javamodel';

transformation JClass2JPackage(inout javamodel:JAVA);
main () { javamodel.objectsOfType(JClass)->jclass2jpackage();}
mapping JClass::jclass2jpackage() : JPackage /*()*/{
init {
result := resolveIn(JClass::jclass2jpackage,JPackage)
->select(p|self.packageName=p.name)->first();
--if (result <> null) return;
}
name := self.packageName;
}

I am defeated by the "if result then return" line.

It seems that we must use () to force the imperative rather than declarative if.

Presumably we need "<> null" to ensure a Boolean condition, but Eclipse QVTo doesn't complain about this, perhaps other bugs occlude this warning.

A value-less return is diagnosed as an error so I tried "return result", so that:
 
The premature return is diagnosed as not supported by Eclipse QVTo.

Iff the premature return is really needed, then the missing support in Eclipse QVTo is bad.

But I don't understand the resolveIn at all, the second argument seems optional and undocumented. Is it an optional predicate on the return value?

The semantics of the init look very important and suspect. Presumably the resolveIn target is created before/as the init executes but even if it does, surely, JPackage::name is uninitialized so that ->first() must always return invalid since the name match fails and no successful mapping ever executes?

------

Third example using late resolve seems fine apart from typos.

------

I cannot make the fourth two-pass variant work. After changing (UML2JavaTwoPass.qvto)

transformation Uml2Java(in uml:UML,out java:JAVA)
main() : JAVA::Interface {
uml->objectsOfType(Class)->map transformClass();
uml->objectsOfType(Class)->map transformClassInheritance();
}
mapping UML::transformClass() : JAVA::Interface {
name := "Ifce".concat(self.name);
}
mapping UML::transformClassInheritance() : JAVA:Interface {
base := self.superClass->resolveIn(transformClass,JAVA::Interface);
}

to

modeltype JAVA uses 'http://www.omg.org/qvt/examples/javamodel';
modeltype UML uses 'http://www.omg.org/qvt/examples/umlmodel';

transformation Uml2Java(in uml:UML,out java:JAVA);

main() /*: JAVA::Interface*/ {
uml.objectsOfType(Class)->map transformClass();
uml.objectsOfType(Class)->map transformClassInheritance();
}
mapping UML::Class::transformClass() : JAVA::Interface {
name := "Ifce".concat(self.name);
}
mapping UML::Class::transformClassInheritance() : JAVA::Interface {
init{
result := resolveIn(UML::Class::transformClass,JAVA::Interface)->first();
}
result.base := self.superClass.resolveIn(UML::Class::transformClass,JAVA::Interface);
}

I am unable to persuade the second pass to re-use the first.

Can anyone help? Is it an Eclipse QVTo bug?

    Regards

        Ed Willink