CZ: multiple inheritance without diamonds

Multiple inheritance has long been plagued with the “diamond” inheritance problem, leading to solutions that restrict expressiveness, such as mixins and traits. Instead, we address the diamond problem directly, considering two difficulties it causes: ensuring a correct semantics for object initializers, and typechecking multiple dispatch in a modular fashion—the latter problem arising even with multiple interface inheritance. We show that previous solutions to these problems are either unsatisfactory or cumbersome, and suggest a novel approach: supporting multiple inheritance but forbidding diamond inheritance. Expressiveness is retained through two features: a “requires” construct that provides a form of subtyping without inheritance (inspired by Scala [40]), and a dynamically-dispatched “super” call similar to that found in traits. Through examples, we illustrate that inheritance diamonds can be eliminated via a combination of “requires” and ordinary inheritance. ...

• Type: Conference
• Year: 2009
• Where: OOPSLA
• Authors: Donna Malayeri, Jonathan Aldrich
• Keywords: Inheritance Problem, Multiple Inheritance, Multiple Interface Inheritance, OOPSLA 2009, Security Privacy