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From: "G.B." <bauhaus@futureapps.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Declaring constants for a abstract tagged type and concrete sub
 classes
Date: Mon, 6 Jul 2015 19:36:59 +0200
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Date: 2015-07-06T19:36:59+02:00
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On 06.07.15 15:49, Serge Robyns wrote:

>> In case you can afford a publicly abstract but
>> privately non-abstract type,
>>
>> package Abstract_Root is
>>      type T_Root is abstract tagged  private;
>>      procedure Set_XYZ (Self: in out T_Root; ABC : in Integer);
>>      function Get_XYZ (Self: in T_Root) return Integer;
>>      No_Element : constant T_Root;  -- or T_Root'Class;
>> private
>>      type T_Root is tagged record
>>         XYZ : Integer;
>>      end record;
>>      No_Element : constant T_Root := T_Root'(Xyz => 666);
>> end Abstract_Root;
>>
>> Every object needs to be of a concrete type, whether constant
>> or not. (...)

> Seems not to work as expected, at least not on GNAT 2015.

Just FTR, this is a working example, tested with GNAT 2015;
did you change T_Root to concrete in the private part of
Abstract_Root, leaving it abstract only in the public part?
Is your constant No_Element perhaps declared outside Abstract_Root?

 > If I use No_Element : constant T_Root; => I get "type of object 
cannot be abstract" compile error