Re: Generics vs. O-O?

[Georg Bauhaus <rm.dash-bauhaus@futureapps.de>]

On 01.08.13 21:24, Dmitry A. Kazakov wrote:

> 7. Formal generic types of Ada are weakly typed. Matching is by structure.
> User-defined generic types (ADTs) are not supported. User-defined
> operations on formal types are not supported. The language of formal
> generic parameters is somewhere between FORTRAN-IV and K&R C.

Not quite far from a misrepresentation of Ada generics.
Nothing in the languages mentioned can require type equivalence
by name in whatever generic formals, as in

package N is

   type T is range -1 .. 1;

   generic
     type S is new T;
   package Pointless is end;

   type Q is range -1 .. 1;

   package Exmpl is new Pointless (Q);  -- error

end N;

Equivalent structure of scalar types T and Q won't do.

> 9. Generic units are basically non-testable. Substitutability issues are
> difficult to verify because of 7.

With generics, substitutability issues arise as soon as one wishes to subsume
the mechanism of generic units under a formally extraneous type systems.
So, judicious use of this language features for things other than typing
might be the better choice.


In general, attributing "weakly typed" to languages will profit
from being done in a more detailed, more informative, and therefore
more convincing  way. The C example

struct A {};
struct B {};

int f(struct A x) {}
int g(struct B y) {}

void test()
{
   f((struct B){});  /* compile time type error */
}

shows that C is not entirely weakly typed!