Re: Subtype predicates

[Shark8 <onewingedshark@gmail.com>]

On Wednesday, August 24, 2016 at 3:18:47 PM UTC-6, Anh Vo wrote:
> On Wednesday, August 24, 2016 at 9:45:52 AM UTC-7, Shark8 wrote:
> > On Wednesday, August 24, 2016 at 7:06:10 AM UTC-6, AdaMagica wrote:
> > > Am Dienstag, 23. August 2016 22:14:30 UTC+2 schrieb Anh Vo:
> > > > type Human_Life_Span_Type is range 0 .. 130 
> > > >   with Default_Value => Human_Life_Span_Type'First;
> > > 
> > > No, I think it's the rule that the name of the entity declared in a declaration (here Human_Life_Span_Type) may not be used again in the same declaration. (You cannot use something that is to be defined recursively in the definition.)
> > > 
> > > I just cannot find the RM chapter and verse.
> > 
> > I think it's different for aspects -- similar that Rosen's Trick the name of the declaration is referent to the instance of the type. So we could say something like:
> > 
> >    -- A string of upper-case letters followed by a single digit.
> >    Subtype ID_String is new String
> >    with Dynamic_Predicate => 
> >      (For all Index in ID_String'Range => 
> >        (if Index /= ID_String'Last
> >         then ID_String(Index) in 'A'..'Z'
> >         else ID_String(Index) in '0'..'9'
> >        )
> >      );
> > 
> > 
> > And since [some] aspects are essentially attribute-specification clauses (eg "Size => 8" = "For T'Size use 8;") there is some sense in thinking it is/should-be legit.
> 
> The 3.5 56.3/3 says that the Default_Value shall be static. Thus, S'First did not comply with Static Semantics. The compiler error should have complained about aspect "Default_Value" requires static expression instead of prefix of "First"... This caused the confusion in the first place.

Why wouldn't 'First (on the discrete-type) be considered Static? It's known at compile-time when the compiler chooses the representation.