An Efficient Implementation of Self, a Dynamically-Typed Object-Oriented Language Based on Prototypes

To compensate for the absence of classes, our system uses implementation-level maps to transparently group objects cloned from the same prototype, providing data type information and eliminating the apparent space overhead for prototype-based systems. To compensate for dynamic typing, user-defined control structures, and the lack of explicit variables, our system dynamically compiles multiple versions of a source method, each customized according to its receiver's map. Within each version the type of the receiver is fixed, and thus the compiler can statically bind and inline all messages sent to self. Message splitting and type prediction extract and preserve even more static type information, allowing the compiler to inline many other messages. Inlining dramatically improves performance and eliminates the need to hard-wire low-level methods such as +, =\x12=, and ifTrue:.

Despite inlining and other optimizations, our system still supports interactive programming environments. The system traverses internal dependency lists to invalidate all compiled methods affected by a programming change. The debugger reconstructs inlined stack frames from compiler- generated debugging information, making inlining invisible to the SELF programmer.

Published as SIGPLAN Notices 24(10), October, 1989. Also published in Lisp and Symbolic Computation 4(3), Kluwer Academic Publishers, June, 1991.

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