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From: "G.B." <bauhaus@notmyhomepage.invalid>
Newsgroups: comp.lang.ada
Subject: A function that cannot be called?
Date: Thu, 18 Oct 2018 14:14:30 +0200
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Xref: reader02.eternal-september.org comp.lang.ada:54627
Date: 2018-10-18T14:14:30+02:00
List-Id: <comp.lang.ada>

There is a type declaration, I rememberd, in Ada, that
does not allow any object of the type to be declared.
I think the type should be along the lines below. Is
this correct?

Then, a function that nominally returns objects of
this type should be impossible to call. Is this right,
too?

generic
     type T(<>) is limited private;  -- gen. arg. type

package What is

     type Void (<>) is private;

     function Impossible (X : T) return Void;

private

     package Inner is
         type Void (<>) is private;
     private
         type Void is  record
             null;
         end record;
     end Inner;

     type Void is new Inner.Void;

end What;

(If current Ada could still pass by reference in both call
direction and return direction, then I'd have added *limited*
to the Voids' declarations. Without it, a body of Impossible
is closer to becoming possible by using Convention => Ada
together with an 'Address clause on a Result object. I think.)