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From: "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: troubles learning OOP: expected type "Parent.Some_Child", found
 type Parent'Class
Date: Mon, 12 Feb 2018 21:25:42 +0100
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Date: 2018-02-12T21:25:42+01:00
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On 02/12/2018 07:17 PM, Mehdi Saada wrote:
> 
>> Get_Elem take T_Token'Class
> How could I do that, since it meant to RETURN a different type for each subclass !

The type-extension way might be

type Something is abstract tagged null record;

function Get_Elem (Token : in T_Token) return Something'Class is abstract;

type Operator_Something is new Something with record
    Operator : T_Operateur;
end record;

overriding function Get_Elem (Token : in T_Token_Operateur) return Something'Class;

Similar extensions of Something and overridings of Get_Elem for other types in 
T_Token'Class. Then Get_Elem (Token_Courant) will dispatch to the appropriate 
Get_Elem.

-- 
Jeff Carter
"You a big nose have it."
Never Give a Sucker an Even Break
107