The one time I've used it seriously was a method that was given the returned body of a HTTP GET call. If I remember rightly it was automatically parsed if it wa

The one time I've used it seriously was a method that was given the returned body of a HTTP GET call. If I remember rightly it was automatically parsed if it was a JSON body, so you could quite rightly get a nil body back, and that wasn't considered an error. However, if the body failed to parse, it invoked this method without an argument (bad decision further up the call stack, but by the point I hit it I didn't have time to refactor around it right then. AFAIK it was changed later to be less shit code and do stuff properly.) So I wanted to know in that method if nil was passed in by argument (as the parsed body was nil), or if no argument was passed, at which point the argument was set to nil as the default value by ruby. Having ruby set a `default = true` if no argument was passed was pretty much the only way to get myself out of that hole right then. Of course, having been coded into that corner once, I'd never do it that way again, so I'm not sure I'll ever be in a corner I need to use it to get out of again. Still useful to have the technique in the back pocket though, just in case!