Mixins in Strongtalk

We describe the use and implementation of mixins [BC90] in the Animorphic Smalltalk system, a high performance Smalltalk virtual machine and programming environment. Mixins are the basic unit of implementation, and are directly supported by the VM. At the language level, code can be dened either in mixins or in classes, but classes are merely sugar for mixin denition and application. The Strongtalk type system supports the optional static typechecking of mixins in an encapsulated manner. Independent of typechecking, the resulting system system substantially outperforms existing Smalltalk implementations.