1.高阶函数基本概念

定义:
1.传入函数的函数或者返回函数的函数
2.函数引用::println
3.带有Receiver的引用 pdfPrinter::println

class PdfPrinter1{
    fun println(any: Any){
        kotlin.io.println(any)
    }
}

object  Hello{
    fun world(any: Any){
        println(any)
    }
}

fun main() {
    val args= listOf("q","w","e","r","t")
    args.forEach(::println)
    args.filter(String::isNotEmpty)
    val pdfPrinter = PdfPrinter1()
    args.forEach(pdfPrinter::println)
    args.forEach(Hello::world)
}