Hi Alex,

can we keep this discussion thread in squeak-dev (and if so then please  
don't reply just to me).

On Thu, 24 Aug 2006 10:55:40 +0200, Alexandre Bergel wrote:

>> Domain a and domain b have precisely the same superclass (oop). So the  
>> answer is: always the right one, since there exists only one  
>> implementor.
>
> It means that a client is always in one (and only one) domain. How those  
> domains are composed each other ?
>
> For instance, a short example of a class Person that has two domains:  
> employee and student.

Initially, "domaining using classes" has only a Person class. This class  
(and all other classes in the same image) belong to the single #system  
domain by default.

When an #employee domain or #student domain is created, instances of  
Person become member of the respective domain as follows:

  employeePerson := (Person clone nowYouClonedClassBelongsToDomain:  
#employee) new.
  studentPerson := (Person clone nowYouClonedClassBelongsToDomain:  
#student) new.

Observe when and where #new is executed. Then,

  (employeePerson domain) printIt => #employee
  (studentPerson domain) printIt => #student

  (employeePerson class) printIt => 'a Person in domain #employee'
  (studentPerson class) printIt => 'a Person in domain #student'

> Person>>employeeDomain.salary
> 	^ 2000
>
> Person>>studentDomain.nbOfCoursesTaken
> 	^ 4
>
> Easy.

I think that our subject "domaining using classes" does not have such  
methods. The methods do not change when domain membership becomes  
effective (i.e. do not have the domainName. prefix from your examples),  
they change neither automagically nor manually.

> the method salary can be invoked by an object x only if x "is" in a  
> domain employee. Same thing for nbOfCourseTaken.
>
> Imagine now the few methods:
>
> "Public methods"
> Person>>employeeDomain.printString
> 	^ self printOn: (WriteStream on: String new).
>
> Person>>studentDomain.printString
> 	^ self printOn: (WriteStream on: String new).
>
>
> Person>>printOn: stream
> 	self generalInfo printOn: steram		"CRITICAL QUESTION HERE"
> 	self description printOn: stream		"CRITICAL QUESTION HERE"
>
> Person>>employeeDomain.description
> 	"Description for being an employee"

An instance of Person in domain #employee does not have the "is an  
employeePerson" property. Instead, it has the "my class belongs to the  
#employee domain" property. This implies that the "domained" Person  
instance belong the their class' domain.

> Person>>employeeDomain. generalInfo
> 	"Description for being an employee"

Same as above.

> Person>>studentDomain.description
> 	"Description for being a student"

Same as above with s/employee/student/.

> Person>>studentDomain. generalInfo
> 	"Description for being a student"

Same as above with s/employee/student/.

> printOn: is not part of any domain (or belongs to a 'default' domain).  
> When printOn: is invoked, how do you know the right method to select ?

Since we have "just" clones of classes, we always select the right method,  
because only that one method exists?

> What does it mean to "be" in a domain ?

Any class can be cloned and the clone is added to a domain (a domain has  
an identifier and a collection of members, i.e. a collection of cloned  
classes). Instances of a domained class belong to their class' domain.

> I am really interested by this discussion!

:)

/Klaus

> cheers,
> Alexandre