scala

问题 I am trying to compose futures with for-comprehension and EitherT, but I am having trouble due the return types. Please can someone explain why this does not compile and how can I make it compile changing the for-comprehension? import scala.concurrent.Future import scala.concurrent.ExecutionContext.Implicits.global import cats.data.EitherT import cats.implicits._ object CatsApp extends App { case class L1(a: String) case class L2(a: String) case class L3(a: String) case class R1(num: Int)

问题 I have an I18N implementation that binds JavaFX UI elements through properties, for e.g.: def translateLabel(l: Label, key: String, args: Any*): Unit = l.textProperty().bind(createStringBinding(key, args)) Having a property binding is easy and works well. However I struggle with ComboBox as it takes an ObservableList (of Strings in my case) and I have no idea how to bind my translator functions to that. I am conflicted about the difference between ObservableValue , ObservableList and Property

问题 I wrote a function to process stream by spark streaming. And I encountered java.lang.NoSuchMethodError: org.json4s.jackson.JsonMethods$.parse$default$3()Z I have checked about the spark version(1.6.0) and scala version(2.10.5). It is consistent with json4s jar version(json4s-jackson_2.10-3.3.0.jar). I can not figure out what happened. And the following is the function code: import org.json4s._ import org.json4s.jackson.Serialization.{read => JsonRead} import org.json4s.jackson.JsonMethods._

问题 I am trying to use Gatling with Kafka, but every so often get this error: 01:32:53.933 [kafka-producer-network-thread | producer-1] DEBUG o.apache.kafka.clients.NetworkClient - Sending metadata request ClientRequest(expectResponse=true, payload=null, request=RequestSend(header={api_key=3,api_version=0,correlation_id=12,client_id=producer-1}, body={topics=[test]})) to node 1011 SLF4J: Failed toString() invocation on an object of type [org.apache.kafka.common.Cluster] java.lang

问题 I am not sure how to get past this "No matching Shape found" error, apart from writing lots of boilerplate. The basic idea illustrated in the Gist is that I have a very basic version of a method (works, but is very specific), then a version that takes the mapper parameter and is more generic (works too, but is specific to one particular type), and then a third version which takes a type parameter and would be very useful, but doesn't compile because of this error. Basic method: def updatePD

问题 How could I transform this: Await.result(purchase, 5 seconds) To be able to write the same statement in the following way: purchase.await(5 seconds) Just trying to learn how to rewrite some of my code by writing my own custom dsl. 回答1: You can create your own implicit class : import scala.concurrent.{Await, Awaitable} import scala.concurrent.duration.Duration object syntax { object await { implicit class AwaitableOps[T](private val awaitable: Awaitable[T]) extends AnyVal { @inline final def

问题 I have some nested maps like: val map1 = Map("key1"->1, "key2"->Map("x"->List(1,2))) val map2 = Map("key3"->3, "key2"->Map("y"->List(3,4))) And I want to merge them to obtain the result map like; val res = Map("key1"->1, "key2"->Map("x"->List(1,2), "y"->List(3,4)), "key3"->3) So nested maps should also be merged. The type of the maps and nested maps can be assumed as Map[String, Any]. It's considered an exception if the two maps have conflict keys (eg. values of the same key are different,

问题 I have yaml file with following details. file name : config.yml - firstName: "James" lastName: "Bond" age: 30 - firstName: "Super" lastName: "Man" age: 25 From this I need to get a spark dataframe using spark with scala +---+---------+--------+ |age|firstName|lastName| +---+---------+--------+ |30 |James |Bond | |25 |Super |Man | +---+---------+--------+ I have tried converting to json and then to dataframe, but I am not able to specify it in a dataset sequence. 回答1: There is a solution, that

问题 Given the following typeclass and some instances for common types trait Encoder[A] { def encode(a: A): String } object Encoder { implicit val stringEncoder = new Encoder[String] { override def encode(a: String): String = a } implicit val intEncoder = new Encoder[Int] { override def encode(a: Int): String = String.valueOf(a) } implicit def listEncoder[A: Encoder] = new Encoder[List[A]] { override def encode(a: List[A]): String = { val encoder = implicitly[Encoder[A]] a.map(encoder.encode)

问题 So I want to write a Fibonacci function in scala that outputs a tree like so: fib(3) | fib(2) | | fib(1) | | = 1 | | fib(0) | | = 0 | = 1 | fib(1) | = 1 = 2 and my current code is as follows: var depth: Int = 0 def depthFibonacci(n:Int, depth: Int): Int={ def fibonnaciTailRec(t: Int,i: Int, j: Int): Int = { println(("| " * depth) + "fib(" + t + ")") if (t==0) { println(("| " * depth) + "=" + j) return j } else if (t==1) { println (("| " * depth) + "=" + i) return i } else { depthFibonacci(t-1