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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Safety of user-defined operators
Date: Sun, 3 Jun 2018 09:58:07 +0200
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Xref: reader02.eternal-september.org comp.lang.ada:52869
Date: 2018-06-03T09:58:07+02:00
List-Id: <comp.lang.ada>

On 2018-06-03 09:39, G.B. wrote:
> On 02.06.18 14:43, Dmitry A. Kazakov wrote:
> 
>> It is semantically problematic because it limits the implementation or 
>> forces a wrong implementation in case of temporal, volatile, shared 
>> objects. A special operator would allow implementation via proper 
>> procedure.
>>
>> It is analogous to automatic dereferencing and indexing. There will be 
>> no solution to until these operations will be done via user-defined 
>> procedure. No number of kludges and obscure helper type will ever 
>> work. Assignment is no different.
>>
> 
> What set of guarantees can user-defined Ada offer, in comparison,
> when users will provide those operations to the compiler that are
> now guarandteed by the language? (Where to "draw the line"?)
> 
> Example:
> 
> - typed, indexed RAM (array),
> 
> as opposed to
> 
> - typed, indexed data structure (user defined).

It is not who provides implementation but what the interface of an array 
is. The difference is between:

    Update (Get_Reference (A, I), V)

and

    Update (A, I, V)

There is no way #1 can handle all important cases of containers and 
there is no way to shape #1 in a way acceptable from the software design 
POV.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de