kotlin 泛型中类型投射

fun main(arg: Array<String>) {
    var ints:Array<Int> = arrayOf(, , )
    val any =Array<Any>(){}
    copy(ints,any)//编译错误,因为Array<Int>不是Array<Any>的子类型

}

fun copy(from :Array<Any>,to:Array<Any>){
    assert(from.size==to.size)
    for (i in from.indices){
        to[i]=from[i]
    }
}

---

fun main(arg: Array<String>) {
    var ints:Array<Int> = arrayOf(, , )
    val any =Array<Any>(){}
    copy(ints,any)//编译通过

}

fun copy(from :Array< out Any>,to:Array<Any>){
    assert(from.size==to.size)
    for (i in from.indices){
        to[i]=from[i]
    }
}

上面是有out类型投射,我们声明的含义:from 不是一个单纯的数组,而是一个被限制投射的数组,也可以使用in关键字来投射一个类型