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大学示例解释了如何更新地图的所有项目：

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

要设置单个项目，可以使用这个繁琐的代码：

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

为了更新单个项目，我写道：

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)

有没有更优雅的语法？

使用列表，选项不是必需的：

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

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

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

或者，更紧凑：

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