From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: User defined implicit conversion
Date: Wed, 30 Oct 2019 23:17:05 +0100
Date: 2019-10-30T23:17:05+01:00 [thread overview]
Message-ID: <qpd251$1ajp$1@gioia.aioe.org> (raw)
In-Reply-To: qpcv5l$sm7$1@franka.jacob-sparre.dk
On 2019-10-30 22:26, Randy Brukardt wrote:
> Implicit conversion itself is the same is eliminating strong typing.
It depends, but arbitrary conversions certainly do.
> If you
> really want that, you probably need to use subtypes rather than types. That
> is, "Type_A" should be a subtype rather than a type.
>
> For example, instead of:
>
> type Type_A is new String;
>
> use:
>
> Subtype Type_A is String;
>
> And now you never need to use a type conversion between Type_A and String.
This is a restriction imposed by Ada 83 in order to be able to generate
such null-conversions. Actually it is not null, a subtype can add a
constraint and then the conversion must include constraint check.
A more general case is when a subtype can have an independent
representation and user-defined conversions:
subtype UTF8_String is String;
-- The conversion must recode Latin-1 to UTF-8
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
next prev parent reply other threads:[~2019-10-30 22:17 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-30 19:43 User defined implicit conversion Alain De Vos
2019-10-30 19:58 ` Simon Wright
2019-10-30 20:39 ` Egil H H
2019-10-30 21:26 ` Randy Brukardt
2019-10-30 22:17 ` Dmitry A. Kazakov [this message]
2019-11-06 6:19 ` G. B.
2019-10-31 11:18 ` AdaMagica
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