CODEWITHSUNDEEP
monocle-scala
Tamriel
Tamriel

Reputation: 1427

Update a single item in a nested case class

The university example explains how to update all items of a map:

(allLecturers composeLens salary).modify(_ + 2)(uni)

To set a single item, one can use this cumbersome code:

(departments composeLens at("History")).set(Some(Department(30, List(Lecturer("arnold", "stones", 30)))))(uni)

To update a single item, I wrote:

def updateBudget(department: Option[Department]): Option[Department] = {
    val budgetLens = GenLens[Department](_.budget)
    Some(budgetLens.set(40)(department.get))
}
(departments composeLens at("History")).modify(updateBudget)(uni)

Is there a more elegant syntax for this?

With Lists, the Optionals are not necessary:

val lecturers = GenLens[Department](_.lecturers)

def updateSalary(lecturer: Lecturer): Lecturer =
    GenLens[Lecturer](_.salary).set(40)(lecturer)

(lecturers composeOptional index(0)).modify(updateSalary)(dep)

Or, even more compact:

(lecturers composeOptional index(0)).modify((l: Lecturer) => l.lens(_.salary).set(40))(dep)

Upvotes: 1

Views: 174

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