Difference between revisions of "Replication"

Revision as of 09:45, 25 August 2006

Work in progress!

We start with some very basic examples, for this we consider all the classes not to be inherited by ANY.

Example set

Basic cases of direct repeated inheritance

The following set of example will base on class B:

class
   B
feature
   f: INTEGER
   g
      do 
         f := f + 1 
      end
end

Three cases of non-conforming repeated inheritance

Lets have look at D1 that repeatedly inherits from B:

class
   D1
inherit {NONE}
   B
      rename f as f1, g as g1 end
   B
      rename f as f2, g as g2 end
feature
end

And an informal description of the semantics: An object of class D1 contains two physical attributes (f1 and f2). A call to feature g1 results in f1 being incremented and a call to g2 increments f2.

Lets do the same for D2:

class
   D2
inherit {NONE}
   B
      rename g as g1 end
   B
      rename g as g2 end
feature
end

An object of class D2 contains one physical attribute (f). A call to either g1 or g2 results in f being incremented.

Class D3 should be rejected by the compiler:

class
   D3
inherit {NONE}
   B
      rename f as f1 end
   B
      rename f as f2 end
feature
end

Since an object of class D3 would have two physical attributes f1 and f2, it is not clear which one g should increment.

Three cases of conforming repeated inheritance

Lets look now at different variants of class D1. They looks exactly as class D1 except that they inherit conforming from B (twice) and therefore need to solve the conflicts between f1-f2 and g1-g2 by selecting. Let DC1_fx_gx be the variant of D1 that selects fx and gx. There are four such variants: DC1_f1_g1, DC1_f1_g2, DC1_f2_g1, DC1_f2_g2.

Even though the following examples contain conforming inheritance, we will start by investigating their semantics in the case where static and dynamic type are equal. When the variants DC1