It's Duck (Typing) Season!

Duck typing provides a way to reuse code and allow a developer to write more extensible code. At the same time, it scatters the implementation of a functionality over multiple classes and causes difficulties in program comprehension. The extent to which duck typing is used in real programs is not very well understood. We report on a preliminary study of the prevalence of duck typing in more than a thousand dynamically-typed open source software systems developed in Smalltalk. Although a small portion of the call sites in these systems is duck-typed, in half of the analysed systems at least 20% of methods are duck-typed.