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Date: Fri, 04 Nov 2011 10:18:10 +0100
From: Georg Bauhaus <rm.dash-bauhaus@futureapps.de>
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Subject: Re: limited allocated classwide types
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Date: 2011-11-04T10:18:10+01:00
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On 04.11.11 00:35, Simon Belmont wrote:
>
> I am only months into being an Ada programmer
> and not trying to anything that isn't well described and ostensibly
> supported, so it seems odd that such a basic test case would uncover
> and compiler bug.  Moreover, one of the points of pride is that Ada
> compilers are heavily tested and verified for safety critical apps,
> which this seems to undercut.

Chances are that a traditional way of ensuring the presence
of operations for a type might work better---if presence is all
that you need(*).

Depending, then, on the intent of the solution, one simple solution
could be to state the expectations where and when they must be met:

generic
    type Has_Doo_Operation is new Has_Doo with private;
package Here_We_Go is
    
    procedure System_Function_1
        (Tool : in out Has_Doo_Operation;
         Stuff : Information'Class);
    
    procedure System_Function_2
        (Tool : in out Has_Doo_Operation;
         Stuff : in out Flour;
         More_Stuff : in out Eggs);
    
end Here_We_Go;

and then ensure things by first deriving concrete Foo_Type from
Limited_Controlled and then passing Foo_Type as actual type for the
abstract type or interface Has_Doo_Operation .

  Or, more flexibly,

generic
    type T is limited private;
    with procedure Doo (This : T);
package Here_We_Go is ...

  Etc.
__
(*) For some old history, rhetoric, emotions, and examples see
http://people.cs.kuleuven.be/~dirk.craeynest/ada-mi.html
(I remember having read the phrase "multiple inheritance bug
has bitten again", somewhere in the Ada archives.)