'Image for composite types

[Martin <martin.dowie@btopenworld.com>]

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