Re: horizontal reuse: traits vs. grafts

On 25.03.2010, at 21:23, Stefan Marr wrote: > Hi: > > > On 24 Mar 2010, at 17:58, Jonathan Bond-Caron wrote: >> One thing I feel is missing from the RFC is how is_a() and instanceof are >> affected with traits or grafts. > Well, my personal (I admit very academic) position is: > - Traits are not classes > - Traits are not interfaces > - Traits are not types > - Traits cannot be instantiated > > Thus, there is no meaning of a is_a and instanceof, and it would not provide any meaningful > information since you can exclude methods from a Trait in a composition. > > Thus, you should resort to interfaces for use-case where you need to ensure that an object > provides a certain set of methods. > > Traits are purely for behavior, the class hierarchy or interface should provide the > type-information/relations. > > >> It's seem to me that a defining a 'trait' should be advertised strictly as >> an 'advanced multiple inheritance technique' to reuse pieces of code and it >> shouldn't be considered as an object (grafts proposal). > It is not an object, right. You can not instantiate traits. > But, I would not speak of multiple inheritance. I would prefer something along the lines of > 'sustainable copy'n'past reuse'. I think Stefan used the right metaphor in the RFC: its language level copy paste. regards, Lukas Kahwe Smith mls@pooteeweet.org