I just had another reminder why I like late binding and flexible typing so much: I had written a handy little utility in Ruby for collecting some data, writing to an open file as data was collected and processed. Initially, I thought: why buffer everything in memory? Then I had the need to use the same functionality to dynamically generate a download from a web app, but I did not have to change any code: I need to collect text and send it out in a Rails controller (instead of using a view) back to a client web browser - I needed in-memory data, not a local file.
Well, since both String and File classes support << (which is what I used in the first version of the code for writing to an open file), I did not have to change any code since I could just pass in an empty string instead of an open file, and return what used to the a file descriptor (instead of closing it) as the value of the accumulated text. Try that in Java or C++ :-)
Anyway, not a big deal, but it did save me refactoring some old code for a new use, saving a few minutes.