From: Trans <transfire@...>
Date: 2007-10-15T19:52:47+09:00
Subject: Re: RubyTraits 0.1



On Oct 15, 5:40 am, "Robert Dober" <robert.do...@gmail.com> wrote:
> Hi list
>
> I have just released ruby-traits v0.1. This are Traits in pure Ruby 1.8.
> Have fun.
>
> ---------------------------------------------------------------------------­-------------
> Traits for Ruby
> ==========
>
>  Traits are Composable Units of Behavior, well that is the
>  academic title,
>
>  For Rubiests the following would be a good definition:
>
>  Mixins with Conflict Resolution and a Flattening Property
>  allowing to avoid subtle problems like Double Inclusion and
>  calling method x from Mixin L while we wanted method x from
>  Mixin N.
>  There is some (extra/nice?) composition syntax too
>
>  For details please refer to:
>    http://portal.acm.org/ft_gateway.cfm?id=1028771&type=pdf&coll=GUIDE&d...
>  which is a PhD thesis defining traits formally.
>
>  And yes Traits are implemented in Squeak 3.9.
>
>  In practice Traits enable us to:
>  * get a RuntimeError when we call a method defined by
>    more than one trait.
>    These conflicts can be resolved by redefining the method.
>  * avoid any double inclusion problem.
>  * compose Traits
>  * alias methods during Trait Composition
>  * resolve super dynamically (mentioned for completeness, Ruby modules
>    can do this too, of course ;)
>
> Examples:
>   t1 = trait { def a; 40 end }
>   t2 = Trait::new{ def a; 2 end }
>   c1 = Class::new {
>      use t1, t2
>   }
>   c1.new.a  --> raises TraitsConflict
>
>  conflicts can be resolved be redefinition, and aliasing can be used for
>  access to the overriden methods. All this can be combined
>  with traits composition.
>  t = ( t1 + { :a => :t1_a } ) + ( t2 + {:a => :t2_a } )
>  c2 = Class::new {
>     use t
>     def a; t1_a + t2_a end
>  }
>  c2.new.a  --> 42

This is very similar to traits.rb in Facets. But Facets does this with
regular modules, not special Traits class.

So how are you composing these traits? Is it delegation or code
injection?

T.