Re: Ada Interfaces and the Liskov Substitution Principle

[Maciej Sobczak <see.my.homepage@gmail.com>]

On 23 Maj, 23:58, "Randy Brukardt" <r...@rrsoftware.com> wrote:

> > My humble opinion: assignment of class-wide types should be prohibited
> > in the first place. I mean - at compile time.
> > It's just asking for troubles.
>
> That doesn't make much sense. Yes, it is a bit weird that assignment is
> potentially a dispatching operation, but otherwise there is no semantic
> problem with it.

Can it be dispatching on both arguments?
If not, how can you reasonably implement it?

And even if it could, still, how can you *reasonably* implement it?

Let's take a classic example with the hierarchy of geometric objects
(Object, Rectlangle, Triangle, Circle, and so on) and this:

procedure Do_Something(X : in Object'Class; Y : out Object'Class) is
begin
  Y := X; -- ?
end Do_Something;

> (The OP having an illegal example, thus proving nothing.)

The OP did not prove that Ada violates LSP, but he did point out where
the problems can hide.

Coming from C++, I have never seen any single example where assignment
made sense with polymorphic hierarchies.

Do you know any such example? Can you show it?

> It might be a bit hard to use usefully, but that's no reason for banning it.

C programmers can use the same logic to justify everything. ;-)

--
Maciej Sobczak
http://www.msobczak.com/