高阶函数的一些用法和理解

//map源码
fun <T, R> List<T>.map1(transform: (T) -> R): List<R> {
        val result = arrayListOf<R>()
        for (item in this)
            result.add(transform(item))
        return result

    }
//演示list
    var ints = asList(1, 10, 20, 30)
    val doubledList = ints.map { it -> it * 2 }
    println("double list:"+doubledList);
// index =0  item[0]=1 1*2=2  2. 20 .40 60  double list:[2, 20, 40, 60]

//高级一点的

    val fruits = listOf("banana", "avocado", "apple", "kiwi","bbaaaa")
    fruits
            .sortedBy {it  }
            .filter { it.startsWith("a") }//只需要a开头的
            .map { it.toUpperCase() }//all upper//并转换为大写
            .forEach { println("current ${it}") }//after print
//上面的高阶顺序基本上不可以调整否则语法报错