Re: [boost] [qvm] deduce_xx traits wouldn't introduce ODR issues.

Subject: Re: [boost] [qvm] deduce_xx traits wouldn't introduce ODR issues.
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2015-12-28 19:30:17

Le 23/12/2015 23:44, Adam Wulkiewicz a écrit :
> Emil Dotchevski wrote:
>> On Wed, Dec 23, 2015 at 6:24 AM, Adam Wulkiewicz 
>> <adam.wulkiewicz_at_[hidden]>
>> wrote:
>>
>>> Vicente J. Botet Escriba wrote:
>>>
>>>> Le 10/12/2015 08:30, Emil Dotchevski a écrit :
>>>>
>>>>> On Wed, Dec 9, 2015 at 10:36 PM, Vicente J. Botet Escriba <
>>>>> vicente.botet_at_[hidden]> wrote:
>>>>>
>>>>> Le 10/12/2015 00:15, Emil Dotchevski a écrit :
>>>>>> On Wed, Dec 9, 2015 at 2:51 PM, Vicente J. Botet Escriba <
>>>>>>> vicente.botet_at_[hidden]> wrote:
>>>>>>>
>>>>>>> The problem appear when two such programmers do it (think of 3pp).
>>>>>> If within one program two programmers introduce two different
>>>>>> definitions
>>>>>>
>>>>> under the same name, yes you have ODR but that is hardly a library
>>>>> problem.
>>>>> :)
>>>>>
>>>>>
>>>>> Hmm. This is a library issue, because the library provides an 
>>>>> interface
>>>> that allows to configure types that don't know each other by two 
>>>> different
>>>> parts.
>>>>
>>>> TBoost.Conversion was rejected exactly by this reason.
>>>>
>>> This indeed is an important point, unfortunately I cannot take it into
>>> account because it wasn't mentioned in any review.
>>> Vincente, do you plan to write one?
>>>
>> If the problem is that QVM allows you to specialize a type template, and
>> that it is possible for two programmers to introduce two different
>> definitions for the same specialization, how is that a library issue? If
>> that's a problem then we can't allow any templates in any library
>> interface, which seems odd.
>
> Basically I think we should clarify this. AFAIU the problem might 
> occur if there were e.g. two libraries (abc and def) providing their 
> own matrix representations (e.g. abc::mat4x4 and def::mat4x4). Then 
> we'd have two other libraries (X and Y) both using those two matrix 
> types together with QVM. So both X and Y libraries would have to 
> specialize QVM traits for abc::mat4x4 and def::mat4x4. Then, if both X 
> and Y libraries were included in a program there would be problems 
> since the specializations of QVM traits would be duplicated. I'm not 
> sure if we could do anything about it because similar problem would 
> occur every time when any traits was required by any library. So AFAIU 
> this is what Emil is saying.
>
> Or are deduce_xx traits somehow different than other QVM traits?
>
> Vincente is this what you had in mind or was it a different issue?
>
>
Hi,

yes, this is exactly the case.

Vicente