Re: Ada.Strings.Bounded

[Adam Beneschan <adam@irvine.com>]

On Apr 21, 5:49 pm, Adam Beneschan <a...@irvine.com> wrote:

> >     -- (Example C)
> >     Z0 : constant := Integer'Last ;
> >     type Z is range 0 .. Z0 ;
> >     B : constant Z := ( Z0 + 1 ) - 1 ;

> > All the above examples seem to indicate that GNAT, at least, is
> > resolving overloaded addition operators.  The overload is between the
> > declared type, root_integer (or something like it), and possibly even
> > universal_integer.  With other types, ones where there is no universal
> > type, this would be an illegal ambiguity.  So it seems that GNAT is
> > nondeterministically resolving them.
>
> There's nothing nondeterministic about this.  See 8.6(29).

I goofed.  This rule doesn't actually apply in this case, since the
expected type of the expression is a user-defined integer type, which
isn't compatible with root_integer.  (If the expected type of an
expression is a specific integer type that isn't root_integer, the
expression can be of that type or it can be universal_integer, but it
can't be root_integer.)  I've sometimes made the mistake of confusing
root_ and universal_integer, and I got sloppy here.

But I think that actually makes the point even moreso that there's no
nondeterminism involved.  The expected type is Z; therefore, in
example C, the only possible meaning for "-" is the function that
takes two arguments of type Z and returns Z.  That, in turn, applies
to "+".  So it's 100% clear from the language rules what functions are
called by this expression.  The reason it doesn't raise
Constraint_Error is 4.9(33), as I mentioned earlier.

                                 -- Adam