For this, create a class called CallSiteInfo and specify the return type as being that class, like this:

In ClassSiteInfo.scala:

    private[spark]
    class ClassSiteInfo(val lastSparkMethod: String, ...)

And here:

    def getCallSiteInfo: CallSiteInfo = {

We try to include return types in all of our method signatures so that we get a warning if we ever change the code to return another type.