Resolve conflict between inheritance and mixins
Some in the Ruby community (like Chad Fowler) have noticed issues around how Ruby attempts to transverse a method's pipeline up the inheritance chain. When you inherit a class from another class and then add a mixin, the mixin is not able to supercede the methods defined in the inherited-from class.
I've demonstrated the issue here:
It would be nice if Ruby were to change its default inheritance behavior so that mixin do override a class's methods. Essentially, the behavior would treat inheritance in nearly the same manner that it treats mixins.
class Person < ActiveRecord::Base
would be effectively treated, in a manner of speaking, as:
(I would go so far as to say that we get rid of direct inheritance in favor of always using mixins to accomplish our inheritance goals. I do have a reservation for how this would affect backwards compatibility.)
I dunno if Ruby's current behavior is intentional (having purposeful benefits) but I find it annoying as it makes it difficult to override a behavior in third-party libraries. When I own the classes, I can simply refactor them to prefer mixins as to avoid this issue, but this doesn't solve the dilemma when dealing with vendor libraries.