You're right. I autocomplete Ruby with pabbrev in emacs. Basically it remembers what I wrote and suggests me the strings that match the prefix I'm typing. It's great and more that enough. It can't know the number of arguments I have to pass but it rarely matters. All I usually code in Ruby are Rails apps and they are pretty simple, even the ones with dozens of routes and models. Furthermore the location of classes and files is very predictable. There is no need of an IDE to navigate through the code. I came to think that if a language or a framework needs an IDE there is something wrong with it that the IDE must fix.