Re: Overring function and its returned type

[Adam Beneschan <adam@irvine.com>]

On Friday, November 9, 2012 12:25:17 AM UTC-8, Dmitry A. Kazakov wrote:
> 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.

I don't see that.  It's true that if you define an abstract type T1 with an abstract operation Op, and if you derive an abstract type T2 from T1, Op will be inherited, so it doesn't affect the semantics it you redeclare an abstract Op.  Still, I can certainly understand why a programmer would want to redeclare Op anyway, so that a person reading the package that defines T2 will see all the operations available for T2, and won't have to hunt for the definition of T1 to see what other operations might be defined for T2.  And if the programmer does redeclare Op for T2, then it's a good idea to add the "overriding" keyword to prevent accidents.

Also, it's legal to declare an abstract type derived from a non-abstract type.  In that case, you may actually want to override the non-abstract inherited operation with an abstract one.

                         -- Adam



> 
> 
> 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.
> 
> 
> 
> 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.
> 
> 
> 
> P.S. They should really have used the syntax with the keyword "overriding"
> 
> trailing behind "is" rather than preceding "function/procedure."
> 
> 
> 
> -- 
> 
> Regards,
> 
> Dmitry A. Kazakov
> 
> http://www.dmitry-kazakov.de