Re: Overring function and its returned type

["Yannick Duchêne (Hibou57)" <yannick_duchene@yahoo.fr>]

Le Fri, 09 Nov 2012 09:24:18 +0100, Dmitry A. Kazakov  
<mailbox@dmitry-kazakov.de> a écrit:

> On Fri, 09 Nov 2012 08:13:23 +0100, Yannick Duchêne (Hibou57) wrote:
>
>>            overriding
>>            function F
>>              (E : T)
>>               return R'Class -- Not overriding :-(
>>               is abstract;
>
> What is this? "overriding" + "abstract" does not make sense.

Overriding sometime do nothing, just remind something, recall an inherited  
definition explicitly. Not the same, but a bit comparable to subtyping  
used for type renaming (except I hate the latter and rather like the  
former).

Overriding may also be used to add a postcondition or replace a class wide  
precondition by another.

I you prefer, you can instead think of `P3.F` returning `P3.R'Class`  
instead of `P1.R'Class`, which would be overriding in the strict way you  
expect.

> In any case it is the default. When you do nothing, you get F through
> inheritance and it is abstract when the parent's F was.

I know, but sometime you want something more explicit.

> Ada's declarations are not idempotent, in the sense that you cannot  
> repeat
> them like you could in C++. So "F ... is abstract" always
> overloads/conflicts.

I don't get conflict when it happens I do it, it works fine.

> P.S. They should really have used the syntax with the keyword  
> "overriding"
> trailing behind "is" rather than preceding "function/procedure."

Matter of taste. Personally, it happens I think I would have preferred  
“new” instead of “not overriding”, but I don't mind too much. That's to be  
added to the list of tiny things which may be nice, but not required.


-- 
“Syntactic sugar causes cancer of the semi-colons.” [1]
“Structured Programming supports the law of the excluded muddle.” [1]
[1]: Epigrams on Programming — Alan J. — P. Yale University