Trait mixin

Note: Trait in this sense is different from Rust’s traits.

• Mixin: A Class extension that does not get bound to a specific superclass. Effectively, it’s a class-extension function that transforms some specific classes into other classes. Because the mixin generally assume the class to conform to an interface, this encourages good abstractions.
• Trait: A generalization of mixins, in that multiple extensions are applied at once, with a well-define conflict resolution.