Kotlin 开发 - 双冒号操作符（引用顶层函数、引用成员函数、引用构造函数、引用属性、引用类）

双冒号操作符

1、引用顶层函数

直接引用 ::【函数名】

kotlin 复制代码

fun isOdd(x: Int) = x % 2 != 0

val numbers = listOf(1, 2, 3)

val oddNumbers = numbers.filter(::isOdd)

println(oddNumbers)

kotlin 复制代码

// 等价于

fun isOdd(x: Int) = x % 2 != 0

val numbers = listOf(1, 2, 3)

val oddNumbers = numbers.filter { isOdd(it) }

println(oddNumbers)

2、引用成员函数

未绑定引用 【类名】::【成员函数】

kotlin 复制代码

val list = listOf("a", "bb", "ccc")

val lengths = list.map(String::length)

println(lengths)

kotlin 复制代码

// 等价于

val list = listOf("a", "bb", "ccc")

val lengths = list.map { it.length }

println(lengths)

kotlin 复制代码

data class Person(val name: String, val age: Int)

val list = listOf(Person("Alice", 25), Person("Bob", 30))

val names = list.map(Person::name)

println(names)

kotlin 复制代码

// 等价于

data class Person(val name: String, val age: Int)

val list = listOf(Person("Alice", 25), Person("Bob", 30))

val names = list.map { it.name }

println(names)

已绑定引用 【对象实例】::【成员函数】

kotlin 复制代码

data class Person(val name: String, val age: Int)

val p = Person("Alice", 25)

val nameGetter = p::name

println(nameGetter())

3、引用构造函数

kotlin 复制代码

data class Person(val name: String, val age: Int)

val createPerson = ::Person

val p = createPerson("Alice", 25)

println(p)

4、引用属性

kotlin 复制代码

var count = 0

fun main() {
    val countProperty = ::count

    println(countProperty.get())

    countProperty.set(5)

    println(count)
}

对于局部变量，Kotlin 编译器不支持生成可修改的属性引用，只能生成只读的引用

kotlin 复制代码

fun main() {
    var count = 0

    val countProperty = ::count

    println(countProperty.get())

    countProperty.set(5)

    println(count)
}

复制代码

# 输出结果

Unresolved reference 'set'.

5、引用类

kotlin 复制代码

data class Person(val name: String, val age: Int)

val kClass: KClass<Person> = Person::class

println(kClass.simpleName)