Question

In Scala no methods can be invoked on the current instance when the superclass constructor is called. So there is no opportunity for a method to be invoked which will memorise the value that it is returning, in the current instance. How can I retain the arguments produced to give to a superclass constructor, while still using inheritance, as opposed to composition, and without modifying the source code of the class I’m inheriting from?

Answer 1

In Scala 2.8 and above, use an early definition:

class Foo(arg1: Type1, arg2: Type2) extends {
   val arg3 = new Type3(arg1)
   val arg4 = new Type4(arg2)
} with Bar(arg3, arg4)

This works even if Bar is a class rather than a trait.