Traits are a simple composition mechanism for structuring object-oriented programs. A Trait is essentially a parameterized set of methods; it serves as a behavioral building block for classes and is the primitive unit of code reuse. With Traits, classes are still organized in a single inheritance hierarchy, but they can make use of Traits to specify the incremental difference in behavior with respect to their superclasses.

1. !#$
Lifting your favorite
language with Traits
Alexandre Bergel
RMoD team, INRIA,
Lille, France
alexandre@bergel.eu

2. Outline
1. Limitation of single inheritance
2. Traits
3. Retrospective
4. Freezable Stateful
5. Conclusion

3. Stream in Squeak
• Example of a library that has been in use for
almost 20 years
• Contains many flaws in its design