Re: Ada case-statement

[Jere <jhb.chat@gmail.com>]

On Thursday, March 15, 2018 at 11:37:48 AM UTC-4, Stephen Davies wrote:
> On Wednesday, 14 March 2018 23:16:29 UTC, Randy Brukardt  wrote:
> 
> > declare
> >   Selector : Day_Type renames Calculate_Day;
> >   subtype Weekend_Subtype is Day_Type range Sat .. Sun;
> >      -- Or use a static predicate if the range is discontiguous.
> > begin
> >   case Selector is
> >       when Mon .. Fri =>
> >          ...
> >       when  Sat | Sun =>
> >          ...
> >          case Weekend_Subtype'(Selector) is -- A type conversion works, too.
> >             when Sat =>
> >                ...
> >             when Sun =>
> >                ...
> >          end case;
> >    end case;
> > end;
> 
> Unless this has changed in more recent compilers, the static predicate
> when Sat & Sun are not contiguous does not work. Gnatpro 7.0.2 complains
> about missing values. Also, attempting to use "when Weekend_Subtype" in
> the outer case-statement results in complaints about duplicate values.

I just tried a quick example in GNAT 6.1.1 and 7.2.0 and both seemed pretty
happy with static predicates.  I don't have 7.0.2 to check

procedure jdoodle is
    type Day is (Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday);
    subtype Weekday is Day range Monday .. Friday;
    subtype Weekend is Day
        with Static_Predicate => Weekend in Saturday | Sunday;
        
    v : Day := Monday;
begin
    
    case v is
        when Weekday =>
            case Weekday(v) is
                when Monday    => null;
                when Tuesday   => null;
                when Wednesday => null;
                when Thursday  => null;
                when Friday    => null;
            end case;
        
        when Weekend =>
            case Weekend(v) is
                when Saturday => null;
                when Sunday   => null;
            end case;
    end case;
    
end jdoodle;

no warnings or errors for either version