反射

// 反射

val c = MyClass::class

val c2 = MyClass::class.java

// 获取KClass的引用

val widget: Widget = ...

assert(widget is GoodWidget) { "Bad widget: ${widget::class.qualifiedName}" }

// 函数引用

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

val numbers = listOf(1, 2, 3)

println(numbers.filter(::isOdd)) // prints [1, 3]

// 函数重载时也能使用函数引用

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

fun isOdd(s: String) = s == "brillig" || s == "slithy" || s == "tove"

val numbers = listOf(1, 2, 3)

println(numbers.filter(::isOdd)) // refers to isOdd(x: Int)

val predicate: (String) -> Boolean = ::isOdd   // refers to isOdd(x: String)

// 实例

fun <A, B, C> compose(f: (B) -> C, g: (A) -> B): (A) -> C {

    return { x -> f(g(x)) }

}

fun length(s: String) = s.length

val oddLength = compose(::isOdd, ::length)

val strings = listOf("a", "ab", "abc")

println(strings.filter(oddLength)) // Prints "[a, abc]"

// 属性引用

// val getter

val x = 1

fun main(args: Array<String>) {

    println(::x.get()) // prints "1"

    println(::x.name)  // prints "x"

}

// var setter

var y = 1

fun main(args: Array<String>) {

    ::y.set(2)

    println(y) // prints "2"

}

// 属性引用用作函数

val strs = listOf("a", "bc", "def")

println(strs.map(String::length)) // prints [1, 2, 3]

// 类成员函数

class A(val p: Int)

fun main(args: Array<String>) {

    val prop = A::p

    println(prop.get(A(1))) // prints "1"

}

// 扩展属性

val String.lastChar: Char

    get() = this[length - 1]

fun main(args: Array<String>) {

    println(String::lastChar.get("abc")) // prints "c"

}