[henshin-dev] Type parameters

[Christian Krause <henshin.ck@xxxxxxxxx>]

Hi,

I thought a bit more about the type parameters problem. I think now that 
it can be very useful and relatively easy integrated into Henshin. Let 
me give you an example. Say we want to model the refactoring 
"PullUpAttribute". Now the idea is that we do not do it for a specific 
metamodel but genericly for a set of types which will be given at 
runtime. Depending on which types we pass to the rule at runtime, we can 
realize the refactoring for, say, Ecore class models or UML class models 
(using the same rule!).

Here is a possible way to integrate it in Henshin. We add a new 0..n 
containment feature called "typeParameters" to the Unit class. The type 
of this reference would be EModelElement. It could be used e.g. to store 
EClasses, EReferences or EAttributes. These types are contained in the 
unit / rule and can be used as types of nodes, edges, attributes or 
parameters. In the runtime, we would add support for setting type 
parameter values in UnitApplication. So if we defined e.g. a type 
parameter "Class" for our refactoring, we could say in the rule 
application that this type parameter should be substituted with the type 
"EClass" from the Ecore metamodel (or "Class" from the UML metamodel).

Cheers,
Christian