Re: troubles learning OOP: expected type "Parent.Some_Child", found type Parent'Class

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

On 02/12/2018 05:29 PM, Mehdi Saada wrote:
> I'm learning POO.

What you're learning is type extension. By far most of the questions on here 
where the language doesn't do what is expected deal with anonymous access types 
and type extension. That's because they're parts of the language that are 
counter-intuitive and confusing. You're doing both. Don't do that, and things 
will be much easier.

But if you're taking a course and have to mess with type extension, at least you 
should avoid the access types.

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

That clearly takes a T_Token_Operateur.

> function TOKEN_COURANT return T_TOKEN'Class is

and that clearly return T_Token'Class, just as the error msg said.

It seems you have 3 choices: Make Get_Elem take T_Token'Class, make 
Token_Courant return T_Token_Operateur, or convert the result of Token_Courant 
to T_Token_Operateur.

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