Lang Martin on Subtyping, Subclassing, and Trouble with OOP

In Subtyping vs. Subclassing (http://okmij.org/ftp/Computation/Subtyping/), Oleg Kiselyov addresses the separation of interface and implementation. The first section shows that in good object oriented design, the type system can't be used in general to decide whether implementations can be safely substituted for one another. In Preventing Trouble (http://okmij.org/ftp/Computation/Subtyping/Preventing-Trouble.html), he outlines a set of rules (in C++) that do allow the type system to enforce subtype relationships, and that look suspiciously familiar.

Lang Martin is a Principal Software Engineer at OpenTable and renown thought-leader in the hand gesture space.