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From: eachus@spectre.mitre.org (Robert I. Eachus)
Subject: Re: overload ":=" ???
Date: 1996/07/24
Message-ID: <EACHUS.96Jul24153824@spectre.mitre.org>#1/1
X-Deja-AN: 169930525
references: <dewar.837740729@schonberg> <4soh73$56h@newsbf02.news.aol.com>
organization: The Mitre Corp., Bedford, MA.
newsgroups: comp.lang.ada
Date: 1996-07-24T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <TARJEIJ.96Jul23153224@ulrik.uio.no> tarjeij@ulrik.uio.no (Tarjei Jensen) writes:

  > The problem with bounded string is that it assigns a global
  > maximum string size instead of letting each string have its own
  > maximum size. The former is not particularly flexible while the
  > latter really require a user defined ":=".

   The generic package Ada.Strings.Bounded can be instantiated as
often as you want.  I have written program which had six
instantiations...  Well, not really.  It had five instantiations which
occured once per program invocation, and a sixth whose size was
determined every time the enclosing procedure was called.

  > Not the least because the maximum length of the strings might be different.

  > e.g:

  >   a : counted_string(4) := "1234";
  >   b : counted_string(5) := "1234";  -- four characters and space for five

  >   a := b;  -- Will not work with current version of Ada

   Try:

   ...
   package Counted is new Ada.Strings.Bounded.Generic_Bounded_Length(10);
   A : Counted.Bounded_String := To_Bounded_String("1234");
   B : Counted.Bounded_String := To_Bounded_String("Some value");
   ...
   A := B; --works fine.
   
   Of couse if instead you say:
   ...
   package Counted4 is new Ada.Strings.Bounded.Generic_Bounded_Length(4);
   package Counted5 is new Ada.Strings.Bounded.Generic_Bounded_Length(5);
   A : Counted4.Bounded_String := To_Bounded_String("1234");
   B : Counted5.Bounded_String := To_Bounded_String("1234");

   Now you have to write:
   ...
   A := Counted4.To_Bounded_String(Counted5.To_String(B));
   
   Of course, if you want, you can make all this less verbose by using
use clauses and perhaps even defining a conversion operation:

   function Convert(B: in Counted5.Bounded_String) 
           return Counted4.Bounded_String is
   begin return Counted4.To_Bounded_String(Counted5.To_String(B)); end;
   pragma Inline(Convert);

--

					Robert I. Eachus

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