OCL 2.0 Type Inference



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brian-l-smith@uiowa.edu
Date: Mon 22 Dec 2003 - 05:52:54 GMT


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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