* troubles learning POO: expected type "Parent.Some_Child", found type Parent'Class
@ 2018-02-12 15:33 Mehdi Saada
2018-02-12 16:35 ` Simon Wright
0 siblings, 1 reply; 2+ messages in thread
From: Mehdi Saada @ 2018-02-12 15:33 UTC (permalink / raw)
I'm learning POO.
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
The definitions:
type T_TOKEN is abstract null record ;
type T_Vect_Token is array (Positive range <>) of access T_Token'Class;
type T_Token_Operateur is new T_Token with
record
L_Operateur : T_Operateur;
end record;
function Get_Elem (Token : in T_Token_Operateur) return T_Operateur is (Token.L_Operateur);
function TOKEN_COURANT return T_TOKEN'Class is
begin
INDEX := INDEX + 1;
return V (INDEX - 1).all;
end;
where V : in T_Vect_Token;
What I do: I declare a T_Token'Class as a local variable. Then, according to the content of the array (V), I do things like this:
when '+' | '-' | '*' | '/'
=> V_LOCAL(INDEX_VECT).all := TO_TOKEN(T_OPERATEUR'Value(STRING'(1 => ELEMENT)));
with a different qualified expression for each sub-classes of Token.
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: troubles learning POO: expected type "Parent.Some_Child", found type Parent'Class
2018-02-12 15:33 troubles learning POO: expected type "Parent.Some_Child", found type Parent'Class Mehdi Saada
@ 2018-02-12 16:35 ` Simon Wright
0 siblings, 0 replies; 2+ messages in thread
From: Simon Wright @ 2018-02-12 16:35 UTC (permalink / raw)
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).
^ permalink raw reply [flat|nested] 2+ messages in thread
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