どういう変換が起こっているのかわからない…

gistfile1.scala

import org.specs2.mutable._

class FunctionArgument {
  def hoge(func: => AnyRef, condition:Boolean = true) : String = {
    if (condition) {
      func.toString
    } else {
      "false"
    }
  }
}

class FunctionArgumentTest extends Specification {
  val target = new FunctionArgument()
  "FunctionArgument " should {
    "hoge can call " in {
      target.hoge("aaa") must_== "aaa"
    }

    "hoge can call to pass false " in {
      target.hoge("aaa", false) must_== "false"
    }

    "hoge can call with func " in {
      def bbb() : String = { "bbb" }
      target.hoge("aaa" + bbb) must_== "aaabbb"
    }

  }
}