Re: Generic Packages

[johnherro@aol.com (John Herro)]

vkire@ERC.MsState.Edu (Kiril Nikola Vidimce) writes:
> ... I was wondering was if I could define a generic
> package with a generic constant/value that would
> be passed when instantiating the package.
     Inside a generic package, generic formal parameters are treated as
constants in any case.  The following example, which works in Ada 83 and
Ada 95, instantiates a generic package with a constant:

generic
   Number : Integer;
package P is
   procedure Show;
end P;

with Text_IO;
package body P is
   procedure Show is
   begin
      Text_IO.Put_Line(Integer'Image(Number));
   end Show;
end P;

with P;
procedure Test is
   I : constant Integer := 3;
   package P3 is new P(Number => I);
begin
   P3.Show;
end Test;

    As expected, the program displays 3, and if you attempt to add the
line
Number := Number + 1;
to procedure Show in the body of P, the compiler will reject the statement
as an assignment to a read-only object.  However, that's still true even
if you remove the word constant from the line
I : constant Integer := 3;
in procedure Test.  The generic formal parameter is treated as a constant
in any case.
     For this reason you can't declare
generic
   Number : constant Integer;
package P is ...

> I am very new in Ada ...
     You've come to the right place!  I hope this helps.  Good luck
learning and using Ada; you'll like it!
- John Herro
Software Innovations Technology
http://members.aol.com/AdaTutor
ftp://members.aol.com/AdaTutor