# Automatic conversion

From: Thomas Baar ^lt;thomas.baar@epfl.ch>
Date: Fri 10 Mar 2006 - 13:34:21 GMT
Message-ID: <4411805D.5060900@epfl.ch>
```D H. Akehurst wrote:

>You can use the invariant
>
>context Department inv:
>   self.person->forAll(salary < self.maxSalaryDept)
>
>In the case where the multiplicity is [0..1].
>
>Using the '->' operator on objects that are not collections automatically wraps
>the object in a Set.
>
>Wraping an undefined value into a set results in an empty set, hence your expression
>gives true when there are no managers.
>
>
Dave,

I'm very puzzled by the automatic conversion to collections, it would mean
that, for example,  5->forAll(x| ...) would be syntactically correct!
What would then be the point to have two different operators '.' (dot) and
'->' (arrow) in OCL? So far, it helped the reader to find out if the source
expression is of object or collection type.

Another question about the emptySet <-> undefined conversion: Wouldn't it be
wise to have the following two constraints equivalent (in case of
multiplicity [0..1]?

context Department inv:
self.person->forAll(...   -- here the object self.person is automatically converted into a collection

context Department inv:
Set{self.person}->forAll(...   -- here the object self.person is manually converted into a collection
-- by wrapping it with Set{  }

Both versions are however not equivalent once that automatic emptySet<->
undefinedness
conversion is adopted. If self is not linked with any other person then
in case
of automatic conversion we had

context Department inv: _emptyset_ -> forAll(...)
what evaluates always to true.

In case of manual conversion we had

context Department inv: Set{_oclVoid_}->forAll(..)
what is not always true.

To summary: The automatic conversion of x into a collection type cannot
be simulated by
Set{x}. However, this would be (at least for me) the most natural
semantics for the automatic conversion...

Best regards,
Thomas

--
Dr. Thomas Baar
Software Engineering Laboratory
School of Computer and Communication Sciences EPFL
EPFL IC UP-LGL
INJ 337 (Bātiment INJ)
Station 14
CH-1015 Lausanne, Switzerland
Tel +41 21 693 2580, Fax +41 21 693 5079
mailto:thomas.baar@epfl.ch   http://lgl.epfl.ch/members/baar/
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```
Received on Fri Mar 10 13:34:54 2006