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Subject: Re: [boost] [review] Conversion - About specialization, overloading and ODR
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2011-09-01 02:48:01

Le 31/08/11 19:21, Roman Perepelitsa a écrit :
> 2011/8/31 Gordon Woodhull<gordon_at_[hidden]>
>> On Aug 31, 2011, at 12:47 PM, Roman Perepelitsa<
>> roman.perepelitsa_at_[hidden]> wrote:
>>> The rule I follow is that operator+(x, x) can be provided only by the
>> author
>>> of x. If xdoesn't have such operator, third parties can't add one. The
>> same
>>> applies to swap and other functions that are expected to be found by ADL
>> and
>>> form the type's interface.
>> If you were defining operator+(X,Y) you'd have the same problem. Any
>> customization point involving two or more types seems to suffer this
>> problem.
> All I'm saying is that customization points requiring two UDTs are bad. I
> would say that a library that promotes them should't be part of boost.
You are surely right as Boost.Conversion need to be especialized for two
types, adn the library has no mean to prevent the user that a bad usage
can fall on ODR violations.

I started this post as I think the same problem could appear for other
Boost libraries with customization points independly of the number of
types. I think that libraries with customization points with one
parameter need to add a warning on the documentation telling the user
that the specific customization of a UDT must be done by the same
library that provides the UDT and that no other library can provide a
customization point for a type provided by a 3rd library.


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