Because Perl5's OO system sucks rocks and is not to be trusted beyond a simple usage. I say this as someone whose CPAN distros are either OO (Tree, PDF::Template, Excel::Template) or OO-related (Perl6::Roles, Class::LazyLoad). Perl5 OO is kinda like the Wizard of Oz - as long as you don't look behind the curtain, everything is ok. The moment you do, even if by accident!, you're completely and utterly screwed. And, the worst part is that you may not realize you're screwed until you lose the client's data.

Adding roles to an introspective OO language that supports aliasing, like Ruby, isn't hard. I may do that for Ruby, now that I'm thinking about it. Ruby's traits.rb isn't Traits, it's a better version of attribute declarations. So, maybe I should call it roles.rb.

Adding it to Perl, however, is way too complicated. Writing Perl6::Roles was a pain in my butt. Not because the code was hard, but because I had to write so much scaffolding and assume so much about how things worked that it made my head hurt. And, that was with punting a whole lot to the user. That's why it's so limited in what it does. There is no attributes, not expectations, or anything. The free-for-all that is Perl's OO actually makes things worse than better.

As for your question - I would gladly use traits/roles/whatever-they're-called-this-week. But, only if they were well-defined. Right now, as Zaxo said, they're an experimental concept. For example:

• Can roles demand certain things? If so, can that be satisfied by another role?
• What happens when conflicts occur?
• What happens when conflicts occur between parent roles? For example, if Class A does roles B and D and role B does C and role D does E. If roles C and E both defined foo(), what happens?
• What happens when role B does roles C and E? Does B have to resolve the conflict? If it does, what's the mechanism? If it doesn't, then doesn't Class A have to know too much about role B?
• Can roles have private methods? How does that work with roles composing roles?
• What happens when role B does role D and role C does role D, then class A does roles B and C? Does this mean that role D conflicts with itself?
• We have class A does role B which provides foo(). Now, instance A1, at runtime, does role C which provides foo(). What now?

Yes, I know a lot of those questions have answers. stvn has done a lot of work in Class::Traits, in his work on the Perl6 metamodel, and in helping me write Perl6::Roles. In all that, he's come up with some darn good answers to a bunch of those questions. That doesn't mean that his answers are complete. And, frankly, his answers may be wrong for some situations.

(Note: stvn doesn't use traits in his production work ... maybe that's a sign that traits aren't ready for primetime.)

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