Re: Indefinite Containers of Indefinite Private Types

["Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>]

On 08/07/2015 01:13 PM, Bob Duff wrote:
> "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org> writes:
> 
>> Yes, of course. The examples are simplified from a more complex case where the
>> container is used in the full type definition. This can be achieved by adding
>> some additional code that is essentially noise, or by using access types.
>> Avoiding access types is worth adding noise, but it would be nice if the noise
>> were unnecessary.
> 
> I'm curious what the "noise" looks like in your case.
> 
> Last time I ran into this problem I think I ended up using a workaround
> that involved access types.  I don't remember the details.

It involves using tagged types, type extension, and a container of a class-wide
type:

with Ada.Containers.Indefinite_Vectors;

package P is
   type T (<>) is private;
private
   type Root is tagged null record;

   package Lists is new Ada.Containers.Vectors
      (Index_Type => Positive, Element_Type => Root'Class);

   type T is new Root with record
      List : Lists.Vector;
   end T;
end P;

The only reason for the type extension is to get the instantiation that can be
used in the full declaration of T. The only objects that will be stored in a
vector are of type T. In addition to the noise of the Root type and the
extension for T, there are type conversions required that are part of the noise.

-- 
Jeff Carter
"From this day on, the official language of San Marcos will be Swedish."
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