Our team lead and I recently discussed the pros and cons of breaking up a long source file into multiple source files. I tend to prefer one class per file, because I find the individual files easier to read and easier to find (with ctrl-p in Sublime). On the other hand, our team lead doesnt have issues with long source files. He argues that they are quite common in open-source projects. As an example, he pointed to the ActionDispatch::Routing::Mapper class in Rails as a case of a long file with multiple inline classes.
I am curious to learn the intent behind keeping all the contents of Mapper class within a single file. What were the advantages of taking this approach?