From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,
	T_FILL_THIS_FORM_SHORT autolearn=ham autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news2.google.com!postnews.google.com!l28g2000vba.googlegroups.com!not-for-mail
From: Martin <martin.dowie@btopenworld.com>
Newsgroups: comp.lang.ada
Subject: 'Image for composite types
Date: Wed, 27 May 2009 15:20:56 -0700 (PDT)
Organization: http://groups.google.com
Message-ID: 
 <f241da28-497c-450a-a804-829eaa1f7608@l28g2000vba.googlegroups.com>
NNTP-Posting-Host: 81.154.95.136
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
X-Trace: posting.google.com 1243462857 22739 127.0.0.1 (27 May 2009 22:20:57
 GMT)
X-Complaints-To: groups-abuse@google.com
NNTP-Posting-Date: Wed, 27 May 2009 22:20:57 +0000 (UTC)
Complaints-To: groups-abuse@google.com
Injection-Info: l28g2000vba.googlegroups.com; posting-host=81.154.95.136;
	posting-account=g4n69woAAACHKbpceNrvOhHWViIbdQ9G
User-Agent: G2/1.0
X-HTTP-UserAgent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US;
	rv:1.9.0.10) Gecko/2009042315 Firefox/3.0.10, Ant.com Toolbar
	1.3,gzip(gfe),gzip(gfe)
Xref: g2news2.google.com comp.lang.ada:6046
Date: 2009-05-27T15:20:56-07:00
List-Id: <comp.lang.ada>

Is it just me that gets fed up with the lack of 'Image on composite
types?

I'm thinking in particular of when I'm testing / debugging and usually
end up writing lots of 'Put_Line' code for each and every record. And
then having to maintain them.

It got me thinking that the language could be expanded to include some
helper attributes for easily composing a function that could return a
String a la 'Image for scalar types.

   function record_type_definition'Component_Name (I : Positive)
return String;
   function record_type_definition'Component_Image (I : Positive)
return String;
   function record_type_definition'Number_Of_Components return
Natural;

   Example
   =======
      type Person is
         record
            Name   : Unbounded_String;
            Age    : Natural;
            Height : Float;
            Weight : Float;
         end record;
   ...
      procedure Put_Line (P : Person) is
      begin
         Put_Line (P.Name);
         for I in 2 .. Person'Number_Of_Components (P) loop
            Put_Line (Person'Component_Name (I) & " => " &
Person'Component_Image (I));
         end loop;
      end Put_Line;
   ...
      Me : Person := (Name   => To_Unbounded_String ("Martin"),
                      Age    => 40,
                      Height => 1.70,
                      Weight => 82.5);
   begin
      Put_Line (Me);
   ...

Gives output:
Martin
Age => 40
Height => 1.70
Weight => 82.5


Or I could define a generic procedure for any of my record types, e.g.

   generic
      type Record_Type is private;
   procedure Put_Line (R : Record_Type);

   procedure Put_Line (R : Record_Type) is
   begin
      -- Notice: no actual names are used at all...
      for R in 1 .. Record_Type'Number_Of_Components loop
         Put_Line (Record_Type'Component_Name (R) & " => "
Record_Type'Component_Image (R));
      end loop;
   end Put_Line;

It might be nice if the language defined a default 'Image for
composites that could be overridden, e.g.

function array_type_definition'Image return String;

   Example
   =======
   type My_Array is array ...;
   for array_type_definition'Image use To_String;

   function To_String (D : My_Array) return String;


function record_type_definition'Image return String;

   Example
   =======
   type My_Record is record ...;
   for My_Record'Image use To_String;

   function To_String (R : My_Record) return String;

Anyone think something like this has legs?

Cheers
-- Martin