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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Unclear error message - please help
Newsgroups: comp.lang.ada
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References: <432C8690.C37D4AE0@alfred-hilscher.de>
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Date: Sat, 8 Oct 2005 23:28:12 +0200
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Date: 2005-10-08T23:28:11+02:00
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On Sat, 08 Oct 2005 21:39:35 +0200, Alfred Hilscher wrote:

> Robert A Duff schrieb:
>> 
>> Don't use Integer all over the place, but instead use
>> different types, to avoid confusion.
> 
> Ok, I tried it, but it seems that a "subtype" is also not the solution:

That cannot have any effect. Subtypes do not resolve ambiguity.
 
> package spec:
> package Pkg is
> 
>   subtype 
>     Sixteen_Bits is Integer range 0..65535;
>     
>   procedure Proc (Host : STRING; RC : out Integer; Identifier : in
> Sixteen_Bits := 0);
> 
>   procedure Proc (Host : STRING;
>                  Time_Response : out Integer; RC : out Integer;
>                  Time_Wait : Integer := 10;
>                  Identifier : in Sixteen_Bits := 0);
> end Pkg;

Why Time_Wait, Time_Response are Integers? Consider making them Time
(absolute time is always more reliable), or maybe Duration (time span) or
at least

   type Milliseconds is new Natural; -- This is not Integer!

Similarly Identifier should be a different type, probably a modular one,
better private.

   type Sixteen_Bits is mod 2**16; 

It could look like:

type ID is private;
No_ID : constant ID;

procedure Proc
          (  Host : String;
             Count : out Natural;
             Identifier : ID := No_ID
          );

procedure Proc
          (  Host : String;
             Count : out Natural;
             Time_Stamp : out Time;
             Time_Out : Duration := 0.01;
             Identifier : ID := No_ID
          );

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de