require 'traits'
#
# a hash argument can be used to specify default values
#
class C
  has 'a' => 4, :b => 2 
end

o = C::new
print o.a, o.b, "\n"

#
# and these traits are smartly inherited
#
class K < C; end

o = K::new
o.a = 40
p( o.a + o.b ) # note that we pick up a default b from C class here since it
               # has not been set

o.a = 42
o.b = nil
p( o.b || o.a ) # but not here since we've explicitly set it to nil