From: Robert Dober <robert.dober@...>
Date: 2007-10-15T18:40:04+09:00
Subject: [ANN] RubyTraits 0.1

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&dl=GUIDE&CFID=7912496&CFTOKEN=77115102
 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