Re: Ada83 equivalents for Ada95

[ncohen@watson.ibm.com (Norman H. Cohen)]

In article <Ds4yxt.7wJ@world.std.com>, bobduff@world.std.com
(Robert A Duff) writes: 

|> And as Brad says, there aren't many problems.  The two *worst* problems
|> are probably:  (1) There are now 256 Characters, instead of 128, and (2)
|> generic formals need a (<>) to accept an unconstrained array.

A third problem right up there with those is that package bodies that are
not required are now forbidden: 

   package Data is
      Table: array (1 .. 100 ) of Float;
      ...
   end Data;

   package body Data is -- legal but dangerous in Ada 83, illegal in Ada 95
   begin
      for I in Table'Range loop
         Table(I) := ...;
      end loop;
   end Data;

There are simple tricks that can be used in Ada 83 to make the package
body required, and hence legal.  Here's one that was posted here
recently: 

   package Data is
      Table: array (1 .. 100 ) of Float;
      ...
   private
      type Package_Body_Needed;
   end Data;

   package body Data is -- legal but dangerous in Ada 83, illegal in Ada 95
      type Package_Body_Needed is record null; end record;
   begin
      for I in Table'Range loop
         Table(I) := ...;
      end loop;
   end Data;

(One can also use a dummy subprogram rather than a dummy type.)

This should be done even in Ada-83 code that will never be ported to Ada
95.  Otherwise, it's too easy to accidently build a system that includes
the declaration but not the body of package Data, meaning that
Data.Table never gets initialized.

--
Norman H. Cohen    ncohen@watson.ibm.com