How to access the resulting output value to perform an upcoming operation for example:

scala> List(1,4,3,4,4,5,6,7)
res0: List[Int] = List(1, 4, 3, 4, 4, 5, 6, 7)

scala> res0.removeDuplicates.slice(0, ???.size -2)

In the above line, i need to perform slice operation after removing duplicates. To do this, how to access output of .removeDuplicate(), so that i can use it to find size for slice operation.

I need to perform this in a single step. Not in multiple steps like:

scala> res0.removeDuplicates
res1: List[Int] = List(1, 4, 3, 5, 6, 7)

scala> res1.slice(0, res1.size -2)
res2: List[Int] = List(1, 4, 3, 5)

I want to access intermediate results in the final operation. removeDuplicates() is just an example.

list.op1().op2().op3().finalop() here i want to access: output of op1,op2,op3 in finalop

Wrapping into into an Option may be one option (no pun intended):

val finalResult = Some(foo).map { foo =>
  foo.op1(foo.stuff)
}.map { foo =>
  foo.op2(foo.stuff)
}.map { foo =>
  foo.op3(foo.stuff)
}.get.finalOp

You can make the wrapping part implicit to make it a little nicer:

object Tapper {
  implicit class Tapped[T] extends AnyVal(val v: T) {
     def tap[R](f: T => R) = f(v)
  }
}

import Tapper._
val finalResult = foo
 .tap(f => f.op1(f.stuff))
 .tap(f => f.op2(f.stuff))
 .tap(f => f.finalOp(f.stuff))