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Recently some of our developers ran into the accusation that with a dynamic language like ruby you use so many dynamic type checks that you end up effectively writing your own type system. So they thought, since we've written a lot of real ruby code - how often do we make dynamic type checks? Michael Schubert gathered up the data.

The table below contains the data. We define a dynamic type check as the use of the methods is_a?, kind_of?, and instance_of?. The lines of code come from the standard rake stats command in rails. (There's an argument that respond_to? and aClass === anInstance should be checked as well, but this is the data I have. The qualitative view is that their use is equally uncommon.)

The moral of this data is that you shouldn't expect to see a lot of type check calls in your ruby code base. This, of course, is true of any dynamic language. It was generally considered bad form in Smalltalk circles I inhabited too.

Most uses are those of dealing with liberal input - eg where a method parameter can be a string, symbol, or array. These crop up in DSLish situations where you want liberal input for the high readability.