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From: Martin <martin.dowie@btopenworld.com>
Newsgroups: comp.lang.ada
Subject: Re: 'Image for composite types
Date: Wed, 27 May 2009 23:46:53 -0700 (PDT)
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Date: 2009-05-27T23:46:53-07:00
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Adam,

Thanks for the comments so far...hopefully there are answers to them
that satisfy...

On May 28, 12:44=A0am, Adam Beneschan <a...@irvine.com> wrote:
[snip]
> This wouldn't work on variant records.

Could add these as well?

   function record_type_definition'Discriminant_Name (I : Positive)
return String;
   function record_type_definition'Discriminant_Image (I : Positive)
return String;
   function record_type_definition'Number_Of_Discriminants return
Natural;

For 'plain' records 'Number_Of_Discriminants would return 0.


>=A0Plus, what does
> 'Component_Image return if the component type is itself another
> record, or an array, or a task? =A0Or an access?

Then it would call the 'Image for that component - in the same way as
for Integer or Float etc.

> Plus, in your example below, one of your components is an
> Unbounded_String, which is a private type most likely implemented as a
> record or access type. =A0What language rule would make 'Component_Image
> of that type return the string value, while 'Component_Image of other
> records or access types would do something more pedestrian?

In this new extension I'm imagining that all records have at least a
compiler generated 'Image (which the user can override) with:

   type My_Record is private;
private;
   fnunction To_String (R : My_Record) return String;
   for My_Record'Image use To_String;

For access types, if I'm writing these by hand, I'd return string
"null" or call the 'Image for the component if it isn't null.


> A lot more thought would have to go into this to make it a real
> language feature.

Absolutely! That's why I'm floating the idea here rather than on Ada-
Comment.

>=A0Others may have opinions on whether the amount of
> effort required to design this feature well, combined with the amount
> of effort required for compiler vendors to implement it, is justified
> by the benefits.

Very true. But I'm pleased to see at least 1 ARG member publicly
acknowledging the problem, if not my proposed solution.

Cheers
-- Martin