A MONOTONIC SUPERCLASS LINEARIZATION FOR DYLAN

Object-oriented languages with multiple inheritance and automatic conf lict resolution typically use a linearization of superclasses to deter mine which version of a property to inherit when several superclasses provide definitions. Recent work has defined several desirable charact eristics for linearizations, the most important being monotonicity, wh ich prohibits inherited properties from skipping over direct superclas ses. Combined with Dylan's sealing mechanism, a monotonic linearizatio n enables some compile-time method selection that would otherwise be i mpossible in the absence of a closed-world assumption. The Dylan linea rization is monotonic, easily described, strictly observes local prece dence order, and produces the same ordering as CLOS when that is monot onic. We present an implementation based on merging and a survey of cl ass heterarchies from several large programs, analyzing where commonly used linearizations differ.