fake lens

2.scala

case class Config(one: Config_1)
case class Config_1(two: Config_2)
case class Config_2(three: Config_3)
case class Config_3(value: Int)

class GetIntService {
  def fromConfig(c: Config): Int
}

def main(config: Config)(service: GetIntService): Int = service.fromConfig(config) + 1

def test: Boolean = {
  val i = 100
  val config = Config(Config_1(Config_2(Config_3(i))))
  main(config)(prod_service) == i + 1
}

// I don't have to make config value here
def test_with_lens: Boolean = {
  val i = 10
  val mock_service: GetIntService = (_: Config) => 10
  main(null)(mock_service) == i + 1
}

default_vs_lenses.scala

case class Config(one: Config_1)
case class Config_1(two: Config_2)
case class Config_2(three: Config_3)
case class Config_3(value: Int)

def real_lens: Lens[Config, Int] = Lens(_.one.two.three.value)

def main(config: Config)(l: Lens[Config, Int]): Int = l.get(config) + 1

def test: Boolean = {
  val i = 100
  val config = Config(Config_1(Config_2(Config_3(i))))
  main(config)(real_lens) == i + 1
}

// I don't have to make config value here
def test_with_lens: Boolean = {
  val i = 10
  val fake_lens: Lens[Config, Int] = Lens(_ => 10)
  main(null)(fake_lens) == i + 1
}