builder pattern.scala

import scala.collection.mutable.ArrayBuffer

type A = ArrayBuffer[Int]

def builder (init: A ?=> Unit) =
  given e: A = new A 
  init
  e

def add(x: Int)(using e: A) =
  e += x

@main def main = 
  println(builder { 
    add(1)
    add(2)
    })