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From: johnherro@aol.com (John Herro)
Subject: Re: overload ":=" ???
Date: 1996/07/18
Message-ID: <4smd11$5bl@newsbf02.news.aol.com>#1/1
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sender: root@newsbf02.news.aol.com
references: <31ED3F5F.1135B4EA@jinx.sckans.edu>
organization: America Online, Inc. (1-800-827-6364)
newsgroups: comp.lang.ada
Date: 1996-07-18T00:00:00+00:00
List-Id: <comp.lang.ada>


David Morton <dmorton@jinx.sckans.edu> writes:
>Is there a way to overload the assignment operator ":=" ?
     Unfortunately, no.  However, you can write your own procedure Assign
or Set.  The difficulty with that is that you may forget to call it, and
use the predefined := instead.
     The workaround is to make the type of the object you're assigning
limited private.  Then the compiler will force you to call your Set
procedure, and won't allow you accidentally to use := (outside the
package).  For example:

package P is
   type Stack is limited private;
   ...
   procedure Set (Left: out Stack; To: in Stack);
end P;

with P; use P;
procedure Main is
   A, B : Stack;
   ...
begin
   ...
   Set(A, To => B); -- Legal
   A := B; -- Illegal.  Compiler will catch this.
end Main;
     There's more information about when to use private types and when to
use limited private types in my Ada Tutor program.  I hope this helps.
- John Herro
Software Innovations Technology
http://members.aol.com/AdaTutor
ftp://members.aol.com/AdaTutor