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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: troubles learning POO: expected type "Parent.Some_Child",
 found type Parent'Class
Date: Mon, 12 Feb 2018 16:35:28 +0000
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Date: 2018-02-12T16:35:28+00:00
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Mehdi Saada <00120260a@gmail.com> writes:

> I have trouble, indeed. Please look at this:
>
> if GET_ELEM (TOKEN_COURANT) = '(' then VALIDE;
> -->
> expected type "T_Token_Operateur" defined
> Found type T_TOKEN'Class

This is because you've declared

> function Get_Elem (Token : in T_Token_Operateur) return T_Operateur
>    is (Token.L_Operateur);

You don't say what T_Operateur is, though it appears to be a Character.

If you declare

> type T_TOKEN is abstract null record ;
   function Get_Elem (Token : in T_Token) return String is abstract;

then Get_Elem is primitive, and you could declare

   function Get_Elem (Token : in T_Token_Operateur) return String;

and you'd get dispatching on the Token parameter when you supply a
T_Token'Class. But that that requires that the Token parameter is in
T_Token'Class and that the other parameters, if any, and the return type
match exactly.

Which gives you a problem since you've stored L_Operateur as a
T_Operateur. You could return (String'(1 => Token.L_Operateur)).

(I'm assuming that other kinds of token could be longer than 1
character).