Re: Preventing type extensions

["J-P. Rosen" <rosen@adalog.fr>]

Le 22/09/2010 19:28, Cyrille a �crit :
>> Because they are unique, coverage testing drops from N to 1.
> 
> No idea of what you are talking about... I suppose this is a reference
> to what OOTiA calls "pessimistic testing" but I still don't understand
> your claim.
> 
Let's take an example:

type T is tagged...;
procedure M1 (X : T);
procedure M2 (X : T);

procedure M1 (X : T) is
begin
   ...
   M2 (T'class (X)); -- Redispatching
end M1;

Under the "big case" model, the dispatching call is equivalent to a case
statement where each branch corresponds to one of the classes that
inherit from T. Therefore, coverage testing will require that M1 (and
similarly every primitive operation that includes at least one
redispatching) be tested for every descendant of T (even if M1 is
redefined by a class D rather than inherited, it is possible to call the
original one with a parameter of type D with a conversion).

If you define:
procedure M2_Class (X : T'class) is
begin
   M2 (X);
end M2_Class;

and replace every redispatching call to M2 by a call to M2_Class, then
the big case disappears. You need (of course) to check coverage for
M2_Class, but M1 needs to be checked only for values of type T, not for
descendants. That's what I meant when I said that coverage testing drops
from N to 1

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           J-P. Rosen (rosen@adalog.fr)
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