//閉包
//函式執行的環境就是閉包
//持有函式的執行環境
//函式內部可以定義函式 也可以定義類
val string = "hello world"
fun makeFun():()->Unit{
    var count = 0
    return fun(){
        println(++count)
    }
}
fun fibonacci():()->Long{
    var first = 0L
    var second = 1L
    return fun():Long{
        val result = second
        second+=first
        first = second-first
        return result
    }
}
fun fibonacci1(): Iterable<Long> {
    var first = 0L
    var second = 1L
    data class Person(val name:String)
    return Iterable { 
        object:LongIterator(){
            override fun hasNext() = true

            override fun nextLong(): Long {
                val result = second
                second+=first
                first = second-first
                return result
            }

        }
    }
}

fun add(x:Int)=fun(y:Int) = x+y

fun add1(x:Int):(Int)->Int{
    return fun(y:Int):Int{
        return x+y
    }
}
fun main(args: Array<String>) {
    val x = makeFun()
    x()
    x()
    x()//函式的作用域沒有被釋放 
    
    val f = fibonacci()
    println(f())
    println(f())
    println(f())
    
    for(i in fibonacci1()){
        if(i > 100)break
        println(i)
    }
    var add5 = add(5)
    println(add5(2))
}