Re: Elaboration worries

[Matthew Heaney <matthewjheaney@earthlink.net>]

Robert A Duff <bobduff@shell01.TheWorld.com> writes:

> Yes, that's because generic instantiations are usually at library level,
> and are therefore elaborated at library package elab time.

Just to add to what Bob says here (and to paraphrase what he has recommended in
other threads on this topic), you need to pragma Elaborate_All whenever you do
an instantiation, e.g.

with GP;
pragma Elaborate_All (GP);

package Q is
   pragma Preelaborate; -- or whatever
   package P is new GP (...);
   ...
end Q;

with GR;
pragma Elaborate_All (GR);

package body Q is
  package R is new GR (...);
  ...
end Q;


The Charles library and the GNAT implementation of the standard container
library are implemented like that, with an Elaborate_All on the generic package
being instantiated.

Note that I don't usually bother using pragma Elaborate_Body unless I need to
either force a body for a spec that otherwise wouldn't require a body, or
because the body has state.  In the latter case you want to ensure that the
package state is fully elaborated before any operations in that package are
called (by some other package during its own elaboration).

Of course if, during elaboration of a package, the package calls an operation
in some other package, then the package must Elaborate_All on the called
package.

Normally you want pragma Elaborate_All, but pragma Elaborate is still useful
occasionally, when elaborating packages with mutual dependencies.