重载运算符plus

使用场景：通过+号实现对象属性的叠加

class Test(var num: Int) {
    operator fun plus(t: Test): Test{
        num += t.num
        return this
    }
}

private fun test(){
    val t = Test(1)
    t + Test(2) + Test(3)
    val result = t.num//结果为6
}

理解了plus的原理，还可以通过+号实现链表等

class Test(var next: Test? = null) {
    operator fun plus(t: Test): Test{
        next = t
        return t
    }
}

private fun test(){
    val t = Test()
    t + Test() + Test()
    var sum = 1
    var next = t.next
    while (next != null){
        sum++
        next = next.next
    }
}