How to reload a class or package in Scala REPL?

Question

I almost always have a Scala REPL session or two open, which makes it very easy to give Java or Scala classes a quick test. But if I change a class and recompile it, the RE

Answer 1

Class reloading is not an easy problem. In fact, it's something that the JVM makes very difficult. You do have a couple options though:

• Start the Scala REPL in debug mode. The JVM debugger has some built-in reloading which works on the method level. It won't help you with the case you gave, but it would handle something simple like changing a method implementation.
• Use JRebel (http://www.zeroturnaround.com/jrebel). JRebel is basically a super-charged class reloading solution for the JVM. It can handle member addition/removal, new/removed classes, definition changes, etc. Just about the only thing it can't handle is changes in class hierarchy (adding a super-interface, for example). It's not a free tool, but they do offer a complementary license which is limited to Scala compilation units.

Unfortunately, both of these are limited by the Scala REPL's implementation details. I use JRebel, and it usually does the trick, but there are still cases where the REPL will not reflect the reloaded class(es). Still, it's better than nothing.