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Date: Wed, 19 Dec 2012 13:23:37 +0100
From: Georg Bauhaus <rm.dash-bauhaus@futureapps.de>
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Subject: Re: Press Release - Ada 2012 Language Standard Approved by ISO
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Date: 2012-12-19T13:23:38+01:00
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On 19.12.12 10:38, Dmitry A. Kazakov wrote:
> On Wed, 19 Dec 2012 10:21:51 +0100, Georg Bauhaus wrote:
> 
>> On 19.12.12 10:19, Dmitry A. Kazakov wrote:
>>> It is deeply wrong. A [sub]type should describe some class of entities
>>> sharing common properties and behavior.
>>
>> If properties and behavior are functions of physical time,
>> how does a [sub]type describe the class of corresponding entities?
> 
> They are not.
> 
> The whole idea of typing is to abstract/define/describe properties
> invariant to the program state (and time, and space).

Programmers writing in language Qi might disagree, since their
programs can compute types.

In any case, if a program lets me know whether some predicate
is true for a series of object's states, it gives me a set of
values, filtered, that may be good for making the type more precise
during the next run. Attaching the Dynamic_Predicate as a subtype
constraint draws attention to it; the predicate might otherwise
be hidden in some all too ordinary conditional (no abstraction),
indistinguishable from Boolean functions. A programmer might
prefer to provide a more explicit mechanism for checking, though,
such as by defining an abstract type Filtered, with suitable
operations that triggered when now Dynamic_Predicate is triggered.