Le 31/08/11 19:21, Roman Perepelitsa a écrit :
2011/8/31 Gordon Woodhull<gordon@woodhull.com>
On Aug 31, 2011, at 12:47 PM, Roman Perepelitsa< roman.perepelitsa@gmail.com> 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. Best, Vicente