Lenses example using Monocle http://richashworth.com/2017/06/scrap-the-boilerplate-in-scala-with-lenses

Lenses.sc

import $ivy.`com.github.julien-truffaut::monocle-core:1.4.0`, monocle.Lens
import $ivy.`com.github.julien-truffaut::monocle-macro:1.4.0`, monocle.macros.GenLens

// _.copy fine for simple cases
case class Address(line1: String, line2: String, postcode: String)
val a = Address("221B", "Baker St", "NW1 6XE")

println(a)
println(a.copy(line1 = "221A"))

// Becomes more tedious for nested classes
case class Account(ID: Int, owner: Person)
case class Person(name: String, address: Address)

val p = Person("Sherlock Holmes", a)
val acc1 = Account(1, p)
val acc2 = acc1.copy(
  owner = acc1.owner.copy(
    address = acc1.owner.address.copy(
      line1 = "221A")))

println(acc2)

// Enter Lenses
val owner: Lens[Account, Person]   = GenLens[Account](_.owner)
val address: Lens[Person, Address] = GenLens[Person](_.address)
val line1: Lens[Address, String]   = GenLens[Address](_.line1)

println(owner.get(acc1))
println(line1.set("221A")(a))

// Real power lies in composing lenses
val lens: Lens[Account, String] = owner composeLens address composeLens line1

println(lens.get(acc1))
println(lens.set("221A")(acc1))

Optionals.sc

import $ivy.`com.github.julien-truffaut::monocle-core:1.4.0`, monocle.{Lens, Optional}
import $ivy.`com.github.julien-truffaut::monocle-macro:1.4.0`, monocle.macros.GenLens

import $file.Lenses, Lenses.Address

// Change our domain model so that account owners do not need to provide an address
case class Person(name: String, maybeAddress: Option[Address])
case class Account(ID: Int, owner:Person)

// Set up some example data
val a   = Address("221B", "Baker St", "NW1 6XE")
val p1  = Person("John Watson", None)
val p2  = Person("Sherlock Holmes", Some(a))
val acc = Account(1, p1)

// As before, we can define a lens between account and its owner
val owner = GenLens[Account](_.owner)

// Use `Optional` to manipulate fields of type Option[_].
// Takes two functions as arguments: a 'getter' and a 'setter'
val address = Optional[Person, Address](_.maybeAddress)(a => _.copy(maybeAddress = Some(a)))

println(address.getOption(p1))
println(address.getOption(p2))

println(address.set(a)(p1))

// Lenses and Optionals compose
val optional: Optional[Account, Address] = owner composeOptional address
println(optional.getOption(acc))

val updatedAcc = optional.set(a)(acc)
println(updatedAcc)