Derive Your Dreams 経由で。 http://research.sun.com/projects/plrg/fortress0866.pdf Traits are named program constructs that declare sets of methods. They were introduced in the Self programming language, and their semantic properties (and advantages over conventional class inheritance) were analyzed by Schärli, Ducasse, Nierstrasz, and Black [23]. In Fortress, a method declared by a trait may be eithe