Re: Elaborate_All on child package

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

On 3 Sep., 18:57, "Rego, P." <pvr...@gmail.com> wrote:
> However, should it be done this way? Due to it is already "withed" to the parent package, so why have I make a new with? I mean: why is the following code incorrect:
>    pragma Elaborate_All (Forum_Test);
>    package Forum_Test.Childp is <....>
>
> and why is the following code correct?
>    with Forum_Test;
>    pragma Elaborate_All (Forum_Test);
>    package Forum_Test.Childp is <....>

The simple (and unsatisfying) answer: Because the RM says so.

So your problem is based on lack of understanding of elaboration. A
program begins execution by elaborating all compilation units. There
is no order prescribed for this except that what is mentioned in a
context clause must be elaborated before.

So applied to your example, elaboration order can be:

1. Forum_Test'Spec
2. Forum_Test'Body
3. Forum_Test.Childp'Spec
With this sequence, your program would have worked. However your
compiler, GNAT, chose another sequence:

1. Forum_Test'Spec
2. Forum_Test.Childp'Spec
3. Forum_Test'Body
When Childp calls Construct, you get an elaboration check that fails.

There are several ways to force certain elaboration orders. One is to
use pragma Elaborate_Body in every spec whenever the spec defines a
function - this forces the body to be elaborated directly after the
spec. Sometimes, this is not possible.

Other pragmas are Preelaborate, Elaborate_All, Elaborate, Pure. See RM
10.2.1 Elaboration Control.