Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!ukma!gatech!hubcap!billwolf
From: billwolf@hubcap.clemson.edu (William Thomas Wolfe,2847,)
Newsgroups: comp.lang.ada
Subject: Re: Overloading of assignment
Message-ID: <3667@hubcap.UUCP>
Date: 26 Nov 88 19:59:37 GMT
References: <881125130910.218003ab@elcc.epfl.ch>
Sender: news@hubcap.UUCP
Reply-To: billwolf@hubcap.clemson.edu
Lines: 31

From article <881125130910.218003ab@elcc.epfl.ch>, by madmats@elma.epfl.ch (Mats Weber):
! Consider the following example:
! 
#    package ADT is
#       type T is limited private;
#       procedure ":=" (OBJECT : in out T; VALUE : in T);
$       function TO_T (N : INTEGER) return T;
$    private
$       type T is range 0..1000;
%    end ADT;
% 
%    with ADT; use ADT;
&    procedure P is
&       X : ADT.T;
*    begin
*       X := TO_T(7);    -- this call of ":=" is erroneous because X
*    end P;              -- is undefined.

 The solution is to enable any type of object to be automatically initialized;
 any type of object should be able to carry the value "undefined", which is
 automatically assumed by all objects not otherwise initialized.  

 The value "null" would be an alias for "undefined", to preserve compatibility.

 In the case of integers, for example, we typically have the range
    31    31                            31        31
  -2  .. 2  - 1; this would shrink to -2  - 1 .. 2  - 1, using the
                      31
 liberated value of -2  as our representation of "undefined", and
 rendering the range of an integer symmetrical, thus eliminating
 the problem of having -1 * MAXINT raise a NUMERIC_ERROR.