From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Why doesn't Ada allow user-defined attributes?
Date: Sat, 22 Jul 2017 22:12:51 +0200
Date: 2017-07-22T22:12:51+02:00 [thread overview]
Message-ID: <ol0bk1$7et$1@gioia.aioe.org> (raw)
In-Reply-To: okvuh3$o1h$1@dont-email.me
On 2017-07-22 18:33, G.B. wrote:
> On 21.07.17 21:39, Dmitry A. Kazakov wrote:
>> On 2017-07-21 19:11, Georg Bauhaus wrote:
>>> Dmitry A. Kazakov <mailbox@dmitry-kazakov.de> wrote:
>>>> On 21/07/2017 06:46, Georg Bauhaus wrote:
>>>>
>>>>> Do you really need 'Length?
>>>>
>>>> Sure, when for example the result depends on the number of elements.
>>>
>>> Count is computed easily, albeit inefficiently, or even efficiently
>>> whenever a collection type caches its number of elements.
>>> So, is 'Length, if not a static property, more than a prim op?
>>>
>>>> 'Length is a general property of any container (set).
>>>>
>>>>> It seems an implementation detail whenever the language doesn't
>>>>> have forall
>>>>> or exists.
>>>>
>>>> Enumeration requires some additional assumptions, stronger than length.
>>>
>>> What real thing can be counted yet not one by one?
>>
>> Unordered set cannot be enumerated,
>
> https://en.wikipedia.org/wiki/Enumeration
The sixth word there.
>> Lots of external things cannot be, e.g. a file you have no permission
>> to read.
>
> A file needs to have been _counted_ byte by byte,
> or allocated using a known _count_ of bytes, etc.
> in order to have this length.
No. File length is an attribute of a file. You don't need to read file
or to allocate it. You can try it yourself, take an uncompressed movie
file. Reading 4GB takes a *lot* of time, yet file manager shows its size
instantly.
> Permissions don't change this state of affairs.
They prevent reading the file.
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
next prev parent reply other threads:[~2017-07-22 20:12 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-20 0:02 Why doesn't Ada allow user-defined attributes? Shark8
2017-07-20 9:34 ` Brian Drummond
2017-07-20 16:07 ` Shark8
2017-07-21 4:46 ` Georg Bauhaus
2017-07-21 7:08 ` Dmitry A. Kazakov
2017-07-21 17:11 ` Georg Bauhaus
2017-07-21 19:39 ` Dmitry A. Kazakov
2017-07-22 16:33 ` G.B.
2017-07-22 20:12 ` Dmitry A. Kazakov [this message]
2017-07-23 6:41 ` G.B.
2017-07-23 8:22 ` Dmitry A. Kazakov
2017-07-24 17:52 ` G.B.
2017-07-20 18:53 ` Randy Brukardt
2017-07-20 23:58 ` Matt Borchers
2017-07-21 7:14 ` Simon Wright
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