val len = b?.length ?: 0

val result = number.takeIf { it % 3 == 0 }?.let { it / 3 } ?: -1

val user = User("Jack", 20).apply {

  name = "Tom"

  age += 5

}

fun main() = runBlocking {

  GlobalScope.launch {

     delay(100)

     println(" 协程任务执⾏ ")

  }

  println(" 主线程等待 ")

  delay(200)

}

val deferred = GlobalScope.async {

  delay(500)

  " 异步结果 "

}

runBlocking {

  // 此处填写代码获取结果

}

  val job = launch {

     repeat(5) { i ->

        if (!isActive) return@launch

        println(" 执⾏任务 $i")

        delay(200)

     }

  }

  delay(500)

  job.cancel()

}

runBlocking {

  val data = withContext(Dispatchers.IO) {

     // 模拟⽹络请求

     " ⽹络数据 "

  }

  // 切换到主线程更新 UI

  withContext(Dispatchers.Main) {

 println(" 更新 UI:$data")

  }

}