A Case Study on Type Hints in Method Argument Names in Pharo Smalltalk Projects

Abstract—A common practice when writing Smalltalk source code is to name method arguments in a way that hints at their expected type (i.e., aString, anInteger, aDictionary). This practice makes code more readable, but the prevalence of this practice is unknown, thus its reliability is questionable. Tools such as the auto complete feature in the Pharo Smalltalk code editor rely on these hints to improve the developer experience. The default algorithm used in Pharo to extract type information from these hints succeeds in extracting a type in slightly over 36 % of method arguments taken from 114 Pharo projects. In this paper we present the results of analyzing the failing method argument names, and provide several simple heuristics that can increase the rate of success to slightly over 50%. We also present a case study on the relation between type hints and run-time types of method arguments that shows that type hints, in a great majority of cases, reflect run-time types. I