Re: Overlapping ranges

["AG" <ang@xtra.co.nz>]

"Mark A. Biggar" <mark@biggar.org> wrote in message
news:My7Ja.54206$hz1.129990@sccrnsc01...
> AG wrote:
> > Assuming I have a package declaration like this:
> >
> >
> > package range is
> >   type x1 is range 0..255;
> >   type x2 is range 127..2**15-1;
> > end ranges;
> >
> >
> > Is there a way to declare a function
> > using that package that will accept
> > values of either x1 or x2 (and nothing
> > else) restricted to the range 127..255 ?
>
> You have a bug in your design abstraction.

It's not a bug it's a feature  -)

>  x1 and x2 are different
> types and there is no way to declare a parameter with more then one
> type.

Exactly. And that's the problem - I'm looking for a way
to declare a function [and/or whatever] that could handle
values of either of the two [test-bed of course] types and,
on top of that, impose range restrictions on the values passed in.

> First option fix the abstraction:
>
> package range is
>     type xBase is range 0..2**15-1;
>     subtype x1 is xBase range 0..255;
>     subtype x2 is xBase range 127..2**15-1;
>     subtype x1x2Intersect is xbase range 127..255;

Sorry, won't work. V1, V2 and V1x2 of the subtypes
are all mutually assignment-compatible. How would
the function know what you passed in?

> If you really need two separate types:
>
> package range is
>     type xBase is range 0...2**15-1;
>     subtype x1x2Intersect is xBase range 127..255;
>     type x1 is new xBase range xBase'First..255;
>     type x2 is new xBase range 127..xBase'Last;
>
>     function foo(p: x1x2intersect) return ...;
> end ranges;

That's a little bit better but: you've declared
the intersect [sub]type as coming from the type
xBase. What exactly does it have to do with
derived types x1 & x2?

> Another option is to use a discriminated record:

No, sorry, let's not go there. I know it's possible
but it's not exactly what I'm after ...