Re: Optional attributes

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From: Shashank (
Date: Wed 19 May 2004 - 08:29:44 BST

Hi Shane,

Lets suppose I get a serialized object.

Now I have a list of hash codes of objects with different states of same class).

Now when I try to compare hash value of object read from serialized object, and
compare that with existing hash codes it may fail, as the object may have
different state!!. And if this happens then I need to take care against possible
commission fault. And I want to set the state of some object to something.

Now how do I model following requirement
if serialized object is not valid  then set state of some object to something.

Can I use OCL to model that using oclUndefined

context MyClass : readSerialized() :
        let hash :HashCode = self.getObject () in
        if hash.oclIsUndefined() then
        result = this;
        result = that;
    end if

In the above scenario oclIsUndefined()  (Undefined because the hash code created
doesn't matches with existing list of hash code  (Meaning object (serialized
objects) definition is not available to me?)

Is that correct usage of undefined? and correctly distinguishes from the context
of its usage that we are discussing.

Shane Sendall wrote:

> Hi Laurie,
> It is interesting that you differentiate between "never been
> initialized" and "uninitialized". Can you whet our appetitte further by
> giving us some examples of where you use this, i.e., some motivating
> examples?
> Thanks,
>     Shane
> Laurence Tratt wrote:
> ><snip>
> >Most languages that I am aware of do not, at the user level, differentiate
> >between "this value has NULL assigned to it" and "this value is undefined" -
> >NULL is all that is given to the user. Note that I am aware of several
> >languages which *internally* have a way of noticing that certain variables
> >and slots have not yet been assigned to, but there's no way for the user to
> >test for this other than causing an exception to be generated. Certainly, my
> >own Converge language follows in these footsteps, so that I can detect
> >people attempting to read from variables before they have been assigned an
> >initial value. Once an initial value has been assigned (be it NULL or
> >anything else), it is impossible for the variable to return to the
> >"undefined" state.
> >
> >Yours,
> >
> >
> >Laurie
> >
> >
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