Scala passing a reference to this class - class

Question

I have a class, with multiple methods and members. When I create an instance of this class, I create an instance of another class within the first class. Some of the methods in this second class require to know which instance of the first class is running. Currently, I am trying to pass "this" into the argument that accepts type firstClass. What am I doing wrong? Again, I simply want the second class instance knowing what first class instance it belongs to so that it can call public methods and members from it.
EDIT: Code example:
def main(args:Array[String]) : Unit = {
val objectOne = new classOne
}
class classOne {
val mutableBuffer = mutable.Buffer[String]
val objectTwo = new classTwo
objectTwo.doThis(this)
}
class classTwo {
def doThis (exA:classOne) = {
exA.mutableBuffer += "Adding text to a Buffer in object One"
}
}

Answer 1

Self-typing is often the cleanest solution here
class Bippy {
outer =>
...
class Bop {
def demoMethod() = println(outer)
}
...
}
UPDATE
The example code changes everything, this clearly isn't about inner classes. I believe your problem is in this line:
val mutableBuffer = mutable.Buffer[String]
It isn't doing what you think it's doing, mutableBuffer is now pointing to the mutable.Buffer singleton, it isn't actually an instance of a Buffer
Instead, try one of these two:
val mutableBuffer = mutable.Buffer[String]()
//or
val mutableBuffer = mutable.Buffer.empty[String]
You should also stick to the convention of starting class/singleton/type names with an uppercase letter, turning your example code into:
import collection.mutable.Buffer
def main(args:Array[String]) : Unit = {
val one = new ClassOne()
}
class ClassOne {
val mutableBuffer = Buffer.empty[String]
val two = new ClassTwo()
two.doThis(this)
}
class ClassTwo {
def doThis(one: ClassOne) = {
one.mutableBuffer += "Adding text to a Buffer in object One"
}
}

Answer 2

I had to make some superficial changes to your example code in order to make it run:
import scala.collection.mutable
class classOne {
val mutableBuffer : mutable.Buffer[String] = new mutable.ArrayBuffer[String]
val objectTwo = new classTwo
objectTwo.doThis(this)
}
class classTwo {
def doThis (exA : classOne) = {
exA.mutableBuffer += "Adding text to a Buffer in object One"
}
}
val objectOne = new classOne
println(objectOne.mutableBuffer(0))
But it works as expected. The classTwo object is able to modify the classOne object. Do you need something beyond this functionality?