Generic child unit renaming

Generic child unit renaming

[noiraud]

I would like to rename Math_Extension an extension of the
generic package Ada.Numerics.Generic_Elementary_Functions.

Thus, I created a generic child unit :

   generic
   package Ada.Numerics.Generic_Elementary_Functions.Extensions is

      function Log10 (X : Float_Type'Base) return Float_Type'Base;

      function Asin  (X : Float_Type'Base) Return Float_Type'Base
         renames Arcsin;

   end Ada.Numerics.Generic_Elementary_Functions.Extensions;

and I tried the following renaming :

   with Ada.Numerics.Generic_Elementary_Functions.Extensions;

   generic package Math_Extension renames
      Ada.Numerics.Generic_Elementary_Functions.Extensions;

The GNAT compiler refused it :

   >>> invalid prefix in selected component "Generic_Elementary_Functions".

I read that renaming is possible if realized in the parent unit, but
I can't do it because Generic_Elementary_Functions belongs to the
predefined library.

Could anyone help me ?

Thanks in advance.

Re: Generic child unit renaming

[dennison]

In article <7fkvbt$q1r$1@ilana.cenaath.cena.dgac.fr>,
  noiraud@cenaath.cena.dgac.fr wrote:
>
>
> I would like to rename Math_Extension an extension of the
> generic package Ada.Numerics.Generic_Elementary_Functions.

My understanding is that users are not allowed to make children of
language-defined units (eg: anything in Ada.*). That would allow you
visibility into the private section of any language-defined unit, which would
allow you to do unspeakable things.

I think Gnat does have a compiler flag to allow you to do it, but unless you
are working on a compiler extension, you probably shouldn't use it.

--
T.E.D.

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Re: Generic child unit renaming

[Matthew Heaney]

dennison@telepath.com writes:

> My understanding is that users are not allowed to make children of
> language-defined units (eg: anything in Ada.*). 

I think the rule is that you can't have _direct_ children of Ada, but
that the language doesn't prohibit indirect children, ie grandchildren
are allowed.

> That would allow you visibility into the private section of any
> language-defined unit, which would allow you to do unspeakable things.

But that's my choice to make.  The language, and the compiler vendor,
should get out of my way.

Re: Generic child unit renaming

[Robert Dewar]

In article <m3k8v0mh3n.fsf@mheaney.ni.net>,
  Matthew Heaney <matthew_heaney@acm.org> wrote:
> But that's my choice to make.  The language, and the
> compiler vendor, should get out of my way.

We constantly run into users who do this sort of thing,
and then yell loudly when their code breaks on a new
release. There is a VERY good reason to prevent this
sort of thing!

Note that the RM specifically allows the implementation
to be restrictive here:

4   The implementation may restrict the replacement of
    language-defined compilation units.  The implementation
    may restrict children of language-defined library units
    (other than Standard).

In GNAT, you must be an implementor to add children to
language defined library units. In particular you have to
obey GNAT style rules and use the -gnatg switch.



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