Re: horizontal reuse: traits vs. grafts

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'. Best regards Stefan -- Stefan Marr Software Languages Lab Vrije Universiteit Brussel Pleinlaan 2 / B-1050 Brussels / Belgium http://soft.vub.ac.be/~smarr Phone: +32 2 629 2974 Fax: +32 2 629 3525