makeObject.swift

func makeObject() -> (getter: () -> String, setter: (String) -> Void) {
    var text = "Hello "
    return (
        getter: { text },
        setter: { text = $0 }
    )
}

let object = makeObject()

print(object.getter()) // "Hello "

object.setter("world!")

print(object.getter()) // "world!"


func makeObject<T>(value: T) -> (T?) -> T {
    var value = value
    return {
        if let newValue = $0 {
            value = newValue
        }
        return value
    }
}

let number = makeObject(value: 1234)

// 取值
print(number(nil)) // 1234

// 存值
number(4321)

// 取值
print(number(nil)) // 4321