Re: (elementary question) Test on type ?

[Mark Biggar <mark.a.biggar@home.com>]

Marin David Condic wrote:
> 
> O.K. O.K. O.K. - You got me there. But that's sort of a deeper technical
> area than what I think the original question was aimed at. (Sounded more
> like a newbie with a more basic question than might be answered by tagged
> records)
> 
> I'd agree that if Ada were more of a "purely OO language" it probably would
> have started deriving all of its types from some base type & generic
> parameters might have had more adaptable characteristics. Its been
> frustrating for me to deal with certain math-oriented packages where I've
> essentially had to create more-or-less identical code for integer types,
> fixed types, floating types and decimal types. Lots of math can be done
> sticking only to the operations common to all of the above and if they were
> all derived from some class called "Scalar" (or had a suitable generic
> formal) you could get there a lot easier.
> 
> MDC
> --
> Marin David Condic
> Senior Software Engineer
> Pace Micro Technology Americas    www.pacemicro.com
> Enabling the digital revolution
> e-Mail:    marin.condic@pacemicro.com
> Web:      http://www.mcondic.com/
> 
> "Ted Dennison" <dennison@telepath.com> wrote in message
> news:le5l7.3173$4z.4905@www.newsranger.com...
> >
> > Actually it is doable, if the type in question is a tagged type. In that
> case
> > you can easily do something like:
> >
> > if Object_A in Parent_Type_X'class then ....
> >
> > The reason this won't work for Integer is that Integer isn't tagged. Thus:
> >
> > 1) You can't use 'Class on it (or a subtype of it).
> > 2) You can't pass it into a routine that can also take other types for the
> same
> > parameter.
> >
> > I suppose you would be able to do that with Integer if Ada had a type
> system
> > where every type was derived from some common root type. I think there are
> some
> > languages out there that work that way. Ada just isn't one of them.
> >

You can do almost what you want using a generic package using a private
generic type and explicitly defining the operators you want to use.
For example if your package only needs "+", "*", "-", "=", "<".

generic
	type Scalar is private;
	with function "+"(Left, Right: Scalar) return Scalar is <>;
	with function "="(Left, Right: Scalar) return Boolean is <>;
	with function "-" ... ;
	with function "<" ... ;
package Special_Math is
	...
end Special_Math;

package Special_Int is new Special_Math(Scalar => Integer);
package Special_Float is new Special_Math(Scalar => Float);

--
Mark Biggar
mark.a.biggar@home.com