Bad GString! Bad! --- Wait, My Bad

I was trying to write a test for a method that inserted some stuff into a StringBuilder that was modified as a GString and was frustrated to find that my stubbed method was never called!

Initially I got mad, blamed Groovy for making my life more difficult with its ridiculous automagical boxing. Then Josh pointed out that StringBuilder is actually a CharSequence. It's not a Groovy thing, I'm just dumb. Fire up your GroovyConsole and observe:

StringBuilder.metaClass.insert = {int arg0, Object arg1 ->
  println "FOOO"
}
StringBuilder.metaClass.insert = {int arg0, String arg1 ->
  println "BARR"
}
StringBuilder.metaClass.insert = {int arg0, CharSequence arg1 ->
  println "I'M HERE!!!"
}

StringBuilder sb = new StringBuilder()
def foo = "ROGER"
def bar = "$foo"
sb.insert 0, bar

The result is "I'M HERE!!!". All I had to do was stub the right method.

If you're experiencing String vs GString issues, like I thought I was, you may find this helpful.