Re: Ada case-statement

[Anh Vo <anhvofrcaus@gmail.com>]

On Thursday, March 15, 2018 at 11:50:19 AM UTC-7, Jere wrote:
> 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

It compiles fine with GNAT-GPL-2017 running on Windows, too.

Anh Vo