From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Tagged type more type safe than access to subprogram ?
Date: Fri, 30 Oct 2009 09:25:12 +0100
Date: 2009-10-30T09:25:09+01:00 [thread overview]
Message-ID: <1u5tn3ocre9xa.mp0ga48bvhg9.dlg@40tude.net> (raw)
In-Reply-To: 4ae9fece$0$6590$9b4e6d93@newsspool3.arcor-online.net
On Thu, 29 Oct 2009 21:45:02 +0100, Georg Bauhaus wrote:
> Dmitry A. Kazakov schrieb:
>> On Thu, 29 Oct 2009 04:00:29 -0700 (PDT), Hibou57 (Yannick Duchêne) wrote:
>>
>>> On 28 oct, 09:55, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
>>> wrote:
>>>> An access to subprogram is a poor-man's closure. Let's ignore "access" part
>>>> and consider a pure downward closure (as it should have been in Ada).
>>
>>> “ As this should have been in Ada ” ? What were you to mean ? I've
>>> always though real closures are not possible with such structures as
>>> Ada provides, except at package level — which is especially the case
>>> when a package can have multiple instances... but only at package
>>> level. Isn't it ?
>>
>> I meant downward closures. [...]
>
>> BTW, in Ada 83, there waa no access to subprogram, so we used tasks instead
>> (where a subprogram had to be a non-generic parameter).
>
> Tagged types may come close to a solution sometimes.
Yes, I am using this pattern very often. But:
1. There were no tagged types in Ada 83
2. In Ada 95 tagged types were in effect strictly library-level. This
restriction was lifted only in Ada 2005, too late to stop the "access-to
everything cancer".
3. The language is too heavy when it comes to create a singleton object
overriding one or two abstract primitive operations. There should be
short-cuts for that.
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
prev parent reply other threads:[~2009-10-30 8:25 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-28 7:51 Tagged type more type safe than access to subprogram ? Hibou57 (Yannick Duchêne)
2009-10-28 8:55 ` Dmitry A. Kazakov
2009-10-29 11:00 ` Hibou57 (Yannick Duchêne)
2009-10-29 17:54 ` Dmitry A. Kazakov
2009-10-29 20:45 ` Georg Bauhaus
2009-10-30 8:25 ` Dmitry A. Kazakov [this message]
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