Re: Non-philosophical definition of Eiffel?

["Matthew Heaney" <matthewjheaney@earthlink.net>]

"Berend de Boer" <berend@xsol.com> wrote in message
news:un0ewiv53.fsf@xsol.com...
> >>>>> "Hyman" == Hyman Rosen <hyrosen@mail.com> writes:
>
> What about this statement:
>
>   "In general, in the design of Charles I have been willing to trade
>   type-safety for flexibility and efficiency."
>
> Telling, isn't it?

What that refers to specifically is the case of "dangling iterators."  If I
do this:

procedure Op (C : in out Container_Type; E : in out Element_Type) is
  I : Iterator_Type;
begin
  Insert (C, E, I);
  Delete (C, I);
  E := Element (I); -- dangling reference
end;

The model in Charles is that an iterator is implemented as a pointer to an
internal node of storage, and it therefore confers no safety benefits beyond
what a plain access type gives you.

To get a completely safe iterator -- one that prevents a dangling reference
from ever occurring-- it is necessary to either reduce flexibility or reduce
efficiency.  But as a library designer, I am an no position to decide how
best to make that trade-off -- only the application developer can know that.
Therefore, my philosophy has been to provide the most flexible and efficient
primitives possible, which can then be combined as desired by the library
user.

We are in agreement that all this business in Java where you have to perform
a downcast when you extract an element is not type safe.  But this is hardly
the case in the STL and in Charles, which provide containers that really are
type safe, unlike Java.

As for a container-of-D being a subclass of container-of-B, this model
doesn't apply to STL or Charles, because those libraries eschew inheritance
in favor of alternate (and simpler) mechanisms.

By using an iterator and a generic algorithm, the container itself
disappears.  So instead of a container-of-D, you have a sequence-of-D, which
is a sequence-of-B, which is the equivalent of a container-of-B.  No
inheritance is necessary, thank you very much.

I'll have another release of Charles ready in the next few days.

http://home.earthlink.net/~matthewjheaney/charles/