Re: Subtype predicates

[Anh Vo <anhvofrcaus@gmail.com>]

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.