An evaluation of tagging

Abstract

Tagging is the augmentation of run‐time data with some form of self‐description for type checking or storage management purposes. We have studied the contribution of automatic tagging by converting two programs written in object‐oriented languages to PL/1. We had thought that much of the apparent superiority of the object‐oriented version came from dynamic binding of operator invocations. However, of several factors contributing to program quality, automatic storage management and the availability of generic abstract data types seem equally important in the examples studied. Tags turned out to be needed for only a few data objects and are used in only a few places. When the obligatory tags are modelled in PL/1, the code becomes particular to the problem at hand and is less elegant. On the other hand, current implementations of object‐oriented languages have considerable overhead in both time and space for tags. This led us to consider combining tagged and non‐tagged objects in a single language. Copyright © 1985 John Wiley & Sons, Ltd