Re: Elaboration circularity with generics

[Adam Beneschan <adam@irvine.com>]

On Jan 15, 9:43 am, AdaMagica <christ-usch.gr...@t-online.de> wrote:
> On 15 Jan., 18:15, Maciej Sobczak <see.my.homep...@gmail.com> wrote:
>
> > In such a case I would consider it to be a compiler bug.
>
> No, this isn't a bug. The elaboration order is not completely defined.
> If the compiler cannot find a valid order, it may reject the program.
> The programmer then has to help the compiler with pragmas.

I think some clarification may help.  There's a rule in 10.2(18) that
says "there shall be a total order of the library_items that obeys the
above rules".  This rule is simple enough that any compiler should be
able to follow it; so if there is a total order and a compiler cannot
find it, the compiler definitely has a bug.

However, the compiler is *not* required to try to find an elaboration
order that will guarantee that Program_Error is not raised at
runtime.  Technically, a program that follows the language rules but
is certain to fail as soon as it's run should not be rejected by the
compiler, since it's a legal Ada program.  But it's useful for
compilers to report errors in such cases.  This may make it "non-
standard" in some sense, but I wouldn't consider it a bug if the
behavior is documented and an option is provided to follow the
standard technically.

                            -- Adam