Re: generic package dilemma

[Mats Weber <matsw@mail.com>]

Matthew Heaney wrote:
> 
> In article <3833F615.5AD7166C@mail.com> , Mats Weber <matsw@mail.com>
> wrote:
> 
> > It does: if the generic instantiates another generic, e.g.
> >
> > generic package P1 is ...
> >
> > generic package P2 is ...
> >
> > with P1;
> > package body P2 is
> >    package P1I is new P1;
> > end P2;
> 
> But isn't this wrong?  Shouldn't P2 elaborate P1?
> 
> with P1;
> pragma Elaborate (P1);
> 
> package body P2 is
>   package P1I is new P1;
> end P2;

Suppose someone else wrote P2 or is still developping it, and that
person does not use pragma Elaborate. With Elaborate_All, you are safe.

> > The clause
> >
> > with P2;
> > pragma Elaborate(P2);
> >
> > does not guarantee that P1's body gets elaborated.
> 
> Is this still true if P2 does the proper thing, and elaborates P1?

No. I totally agree with Robert Dewar here: never use Elaborate, use
Elaborate_All instead.

Your approach of using Elaborate at each level, besides being hard to
enforce on a large project, puts unnecessary constraints on the
elaboration order: in our example, where P2I instantiates P2
instantiates P1, valid elaboration orders are: P1, P2, P2I and P2, P1,
P2I. You are unnecessarily enforcing the first one with your approach.

I have done an extensive study of the shortcomings of pragma Elaborate
in my thesis at
http://lglwww.epfl.ch/Team/MW/Ada-Extensions/Ada-Extensions.html