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From: Georg Bauhaus <nonlegitur@futureapps.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Why doesn't Ada allow user-defined attributes?
Date: Fri, 21 Jul 2017 17:11:28 -0000 (UTC)
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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?