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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Seeking for papers about tagged types vs access to subprograms
Date: Wed, 15 May 2013 22:56:55 +0200
Organization: cbb software GmbH
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Date: 2013-05-15T22:56:55+02:00
List-Id: <comp.lang.ada>

On Wed, 15 May 2013 15:59:07 -0400, Peter C. Chapin wrote:

> Yet who should deal with the structure of, say, a JPEG image?

The implementation of the type if the OS were typed.

> Should every 
> application that wants to manipulate such images duplicate the code 
> required to do so?

The operations of the type could be shared.

> Should the OS materialize the "JPEG file" abstraction 
> directly in its API?

JPEG would implement the interface of some base image type.

It is not much different from how OSes handle drivers. You can register new
driver. A driver belongs to a class of devices (=implements some device
interface, e.g. block device).

The API of a driver is a kind of dispatching operation, e.g.
Read/Write/Open/Close/IOCTL. It is very rudimental and not properly defined
as a type, nonetheless.

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