didSetSemantics.swift

class User {
    var age: Int = 0 {
    didSet { print("didSet for age") }
  }

    var name: String = "" {
    didSet { print(oldValue) }
  }
}

let user = User()
// This will not call the getter to fetch the oldValue
user.age = 15
// This will call the getter to fetch the oldValue
user.name = "name"