Tuesday, May 27, 2014

Groovy fun with @CompileStatic

by Richard Vowles

Groovy is one of the few languages that allow both static and dynamic compilation, and among the "big" languages on the JVM (Java, Groovy, Scala, JRuby and Clojure), the only one as far as I am aware.

Unless I am doing Grails (we stopped at 2.1.13 because of the crazy buggy-ness of that platform, its dependence on Hibernate and just random magic insanity that happens). So just using Groovy in a basic Spring + AngularJS web framework has been empowering - I've only been swapping back to non type safe only really for tests. I still look at Mockito with pain.

One of the things that has bugged me however is Closures. If I wanted a callback to work, I lost the type safety. Consider this method:

  void listProfiles(User user, boolean favourite, String filter, Closure callback)

So I now am not telling the compiler what types are being passed. I thought about this problem tonight and remember that an interface with a single method is treated as a closure - so I thought I'd try it:

    interface ListProfileCallback {
       void profile(Profile profile, boolean favourite)

    void listProfiles(User user, boolean favourite, String filter, ListProfileCallback callback)
and sure enough - the type system kicks in and tells me I'm missing a parameter!

(image taken from http://www.luvyababes.co.uk/)

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