How do I get the IDE to show me constants in an auto-complete fashion

I have some constants defined in an .rb file in the initializers directory. When I use these constants in a piece of code, I expect the IDE to give me a list of the constsants, just like it does syntax, etc. Is there an IDE setting to enable this, or is it not supported?

Environment: Mac IOS 10.7, RubyMine 4.03