Re: "&" for array versus "&" for Strings

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Grein, Christoph" <christoph.grein@eurocopter.com> writes:

> > ------------------------------------------------------------------
> > with Ada.Text_IO; use Ada.Text_IO;
> > procedure Array_Test is
> > 
> >    type Name_Array is array (Positive range <>) of String (1..6);
> > 
> >    procedure Print_Names (Names : Name_Array) is
> >    begin
> >       for No in Names'First .. Names'Last loop
> >          Put_Line (Integer'Image(No) & ": " & Names (No));
> >       end loop;
> >    end;
> > 
> > begin
> > 
> >    Print_Names ("Ada   " & "Babbel");
> > 
> > end Array_Test;
> > ------------------------------------------------------------------
> > 
> > Then the result becomes:
> > 
> >  1: A 2: d 3: a 4:   5:   6:   7: B 8: a 9: b 10: b 11: e 12: l
> > Why is this happening.

Sounds like a compiler bug.

> Which compiler do you use?
> 
> Gnat 3.16w produces an error for this:
> 
> preben.adb:15:17: expected type "Name_Array" defined at line 4
> preben.adb:15:17: found a string type
> 
> With qualification, it works.
> 
>    Print_Names (string'("Ada   ") & string'("Babbel"));
> 
> The problem cause needs an intensive RM exegesis, which I have just not the time 
> for. Could be a compiler error.

That sounds like a different compiler bug.

It seems to me that the "&" should resolve to the
(string, string)-->Name_Array one, even without the "String'(...)"
qualifications.  Apparently, the older compiler resolved it to the wrong
one, and the newer one can't resolve it (which is an improvement, but
still a bug).

I'm not surprised that such a bug has never been noticed before.  Most
people don't write code that uses "&" to concatenate two Strings to
produce something other than String!  First, it's confusing (to humans,
I mean, in addition to compilers).  Second, it requires fixed-length
strings, which is almost never what you want in an array.

- Bob