Re: A bad counterintuitive behaviour of Ada about OO

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> On Thu, 07 Aug 2014 14:14:52 -0400, Robert A Duff wrote:
>
>> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
>> 
>>>...you cannot have one of class-wide
>>> elements.
>> 
>> ...but that's not one of them.  Ada.Containers.Indefinite_Vectors
>> supports class-wide element types, for example.
>
> But you must have class-wide "elementary types" first. There is none, which
> was the point.

Oh, now I see what you mean.  That's not a restriction on generics, it's
a restriction on non-tagged types.  We tried to add 'Class on non-tagged
types in Ada 9X, but the idea was rejected.

universal_integer is something like root_integer'Class, but since you
can't name those types, you can't do something like:

    function Image(X: universal_integer; Base: Integer range 2..16 := 10) return String;

> -----------
> Generics (parametric polymorphism) does not add anything to the language.
> Anything you want to parametrize, must be in the language first, e.g. to
> have a generic package the language must have plain packages.

I think types should be generic, instead.  See Eiffel.

- Bob