Traits

Abstract

This paper describes a new technique for organizing software which has been used successfully by the Xerox Star 8010 workstation. The workstation (WS) software is written in an “object-oriented” style: it can be viewed as a system of inter-communicating objects of different object types. Most of the WS software considers object types to be constructed by assembling more primitive abstractions called traits. A trait is a characteristic of an object, and is expressed as a set of operations which may be applied to objects carrying that trait. The traits model of subclassing generalizes the SIMULA-67 model by permitting multiple inheritance paths. This paper describes the relationship of WS software to the traits model and then describes the model itself.