Re: Elaboration circularity with generics

[AdaMagica <christ-usch.grein@t-online.de>]

On 14 Jan., 23:46, Simon Wright <si...@pushface.org> wrote:
> AdaMagica <christ-usch.gr...@t-online.de> writes:
> > A unit can only be instantiated if it is fully elaborated.
> > I guess GNAT chose the elaboration order P'Spec, P.Q'Spec, P'Body
> > (crash since P.Q'body is not elaborated).
> > This dependence is not present for nongeneric units.
>
> > Perhaps addition of pragma Elaborate_Body to P.Q helps.
>
>    with P.Q;
>    pragma Elaborate (P.Q);          <<<<<<< does the trick for me
>    package body P is

Of course this works, but in my opinion, Elaborate_Body is better
because it has to be applied just once to P.Q, whereas Elaborate has
to be applied on every unit withing P.Q.

As a general rule of thumb I think Elaborate_Body should be applied
whenever a unit provides functions that are used in the spec of other
units providing initial values or constants, such like:

package P is
  pragma Elaborate_Body;  -- prevents elaboration error when F is
called
  function F (...) return T;
end P;

with P;  -- no need for "pragma Elaborate (P);"
package Q is
  V: [constant] T := P.F (...);
end Q;