Re: OCL 2.0 Type Inference



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From: Adrian Carcu (adi1302@yahoo.com)
Date: Mon 22 Dec 2003 - 10:41:34 GMT


Hello,

1. Since both A,B are supertypes of C,D, we can't choose either of them
   as common supertype, so the answer should be OclAny, making the type of
   Sequence{c,d} Sequence(OclAny).

2. 3. 4. If Sequence{c,d} has the type Sequence(OclAny) then the iterator
         v has the type OclAny. Since OclAny.a and OclAny.b do not exist
         any compiler should stop here with a feature not found message.
         Since we have a compilation error I don't think we should talk about
         the expression being undefined. It is simply semantically incorect.

I couldn't find relevant information in the specification to support 1.
The collection literals section present only integer and string collections.
If anyone knows about such information (something formal about how the type
of a collection literal is determined in this case) somewhere else please 
point it to us.

Best regards,
Adrian

> Hi,
> 
> I have some questions about type inference in OCL 2.0. If possible, please
> point
> me to the relevent part of the specification (PTC/03-10-14 or a later
> version).
> 
> Consider these classes:
> 
>      Class A { a : Integer }
>      Class B { b : Integer }
>      Class C subclasses A, B
>      Class D subclasses A, B {
>          cd(c : C, d : D) : Sequence(Integer)
>      }
> 
> And this set of postconditions (please ignore the fact that they are
> inconsistent with each other):
> 
>     context D::cd(c : C, d : D):
>     post A: result = Sequence { c, d }.collect( v | v.b }
>     post B: result = Sequence { c, d }.collect( v | v.a }
>     post C: result = Sequence { c, d }.collect( v | v.a + v.b )
>     
> Questions:
> 
> 1. What is the type of the subexpression Sequence { c, d }? The most specific
> common supertype of C and D is OclAny, so is it Sequence(OclAny)?
> 2. Are postconditions A and B well-typed and well-defined? If the answer to
> question #1 is Sequence(OclAny) then the answer is "no" and "no," right?
> 3. Is postcondition C well-typed and well-defined? I am going to say "no" and
> "no" because there seems to be no way to type the iteration variable.
> 4. I assume it is the case that expressions that are not well-typed are
> undefined; i.e. an OCL expression evaluator is not required to accept any
> expression that it cannot statically typecheck before attempting any
> evaluation.
> Is that correct?
> 
> Thank you,
> Brian


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