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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Your wish list for Ada 202X
Date: Sat, 19 Apr 2014 21:28:03 +0300
Organization: Tidorum Ltd
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Xref: news.eternal-september.org comp.lang.ada:19439
Date: 2014-04-19T21:28:03+03:00
List-Id: <comp.lang.ada>

On 14-04-19 17:21 , Dmitry A. Kazakov wrote:
> On Sat, 19 Apr 2014 16:53:47 +0300, Niklas Holsti wrote:
> 
>> On 14-04-19 13:06 , Dmitry A. Kazakov wrote:
>>> On Sat, 19 Apr 2014 12:08:19 +0300, Niklas Holsti wrote:
>>>
>>>> On 14-04-19 11:39 , Dmitry A. Kazakov wrote:
>>>>> On Sat, 19 Apr 2014 10:19:02 +0200, Dmitry A. Kazakov wrote:
>>>>>
>>>>>> "Re-" presumes that dispatch happens again. What is in common to these two
>>>>>> instances of dispatch what makes it re-dispatch? It is 1) the same
>>>>>> polymorphic operation and 2) the same object. Take either away and it is
>>>>>> not re-dispatch anymore:
>>>>>>
>>>>>> 1. Different operations:
>>>>>>
>>>>>>    X.Foo;
>>>>>>    X.Bar;  -- This is not re-dispatch!
>>>>>>
>>>>>> 2. Different objects:
>>>>>>
>>>>>>    X.Foo;
>>>>>>    Y.Foo;  -- This is not re-dispatch!
>>>>>
>>>>> After some consideration, I take the position 1 back. Operation can be
>>>>> different. But the object must be same.
>>>>
>>>> If we are talking about by-copy types, then whether X and Y are the
>>>> "same object" is fuzzy. Is a copy the same object as the original?
>>>
>>> A copy is another object.
>>
>> Then (by your definitions) redispatching is never possible based on
>> by-copy parameters, because (in your definition) redispatching only
>> occurs if the first and second dispatching call use the same object, but
>> the pass-by-copy in the first dispatching call (in your view) creates a
>> new object which is then used in the second dispatching call.
>>
>> That is a consistent view (good for you) but it disagrees with my memory
>> of your earlier arguments against redispatching, which were based more
>> on the logical redundancy of two successive dispatching calls on the
>> same tag.
> 
> Why does it disagree? 

You are right, it doesn't. I was still thinking about my first
conception of your by-copy method, where the tag would also be copied,
which would allow redispatch. Sorry.

> Arguably, if re-dispatch is impossible for by-copy types when it should be
> made unavailable for by-reference types as well.

As has been made amply clear, I don't share that opinion.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
      .      @       .