scala

问题 I have Sample class with Size annotation case class Sample( attr: SomeTypeA @Size(value = 50) name: SomeTypeB) This Size annotation is a class that implements AnnotationInterface trait AnnotationInterface[T] { def getValue: T } class Size(value: Int) extends StaticAnnotation with AnnotationInterface[Int] { override def getValue: Int = value } And I have Extractor which is responsible for extracting class members using reflection class Extractor[A](implicit tt: TypeTag[A], ct: ClassTag[A] ) {

问题 It seems session variable used in below code is not able to pass the Token Type --> Bearer and access_token using session variable,here is the full code ,is it possible with you to have a look ,here is code provided ..no worries all tokens are dummy tokens as i haven changed before pasting code here.Test expects the login method to be executed first and then the CreatePrivateEvent method as the latter takes tokens from Login method hence i have written From Logs It looks Token Type --> Bearer

问题 as expected reassignment is giving error like below in REPL scala> val a=1 a: Int = 1 scala> a=2 <console>:12: error: reassignment to val a=2 ^ But the below reassignment is not giving error in REPL when a=2 preceded with val. scala> val a=1 a: Int = 1 scala> val a=2 a: Int = 2 When I execute the below code in Intellij its giving error. object Test { def main(args: Array[String]) { val x = 1 val x = 2 } } Why val a=1 and val a=2 are not giving any error in REPL(error if it is only a=2) but

问题 def queens(n: Int): List[List[(Int, Int)]] = { def placeQueens(k: Int): List[List[(Int, Int)]] = if (k == 0) List(List()) else for { queens <- placeQueens(k - 1) column <- 1 to n queen = (k, column) if isSafe(queen, queens) } yield queen :: queens placeQueens(n) } I don't understand how this code works, even tough I debugged in Eclipse. Can you explain step by step this code? By the way, code works correctly. I also understand the n-queens algorithm but I don't understand the mechanism of

问题 I would like to extract the key and value of the head of an HList using these two methods: def getFieldName[K, V](value: FieldType[K, V])(implicit witness: Witness.Aux[K]): K = witness.value def getFieldValue[K, V](value: FieldType[K, V]): V = value I tried a few variations of this function, but I couldn't make it work, I think this might be the closest to the right solution: def getFieldNameValue[Key <: Symbol, Value <: AnyRef, Y <: HList, A <: Product](a : A) (implicit gen : LabelledGeneric

问题 I have an example like this: abstract class IsBaseTC[A] { type Self } abstract class JustHoldsTypeMember[A] extends IsBaseTC[A] implicit val doubleHoldsTypeMember = new JustHoldsTypeMember[Double] { type Self = Double } abstract class IsActualTC[A, T](implicit val aIsBaseTc: IsBaseTC[T]) extends IsBaseTC { type Self = A def get(self: A): aIsBaseTc.Self } case class Container[T]( get: T ) implicit val containerOfDoubleIsActual = new IsActualTC[Container[Double], Double] { def get(self: Self) =

问题 I have an example like this: abstract class IsBaseTC[A] { type Self } abstract class JustHoldsTypeMember[A] extends IsBaseTC[A] implicit val doubleHoldsTypeMember = new JustHoldsTypeMember[Double] { type Self = Double } abstract class IsActualTC[A, T](implicit val aIsBaseTc: IsBaseTC[T]) extends IsBaseTC { type Self = A def get(self: A): aIsBaseTc.Self } case class Container[T]( get: T ) implicit val containerOfDoubleIsActual = new IsActualTC[Container[Double], Double] { def get(self: Self) =

问题 Problem: trait UpperBound[O] trait High[F[O] <: UpperBound[O]] def canEqual(that :Any) = that.isInstanceOf[High[_]] def high(h :High[_]) = ??? Does not compile, because scalac sees the _ type instead of a type constructor it expects. How to fix it, ideally without writing a novel? Original question (before edits in reply to Dmytro's answer) had: def canEqual(that :Any) = that.isInstanceOf[High[m forSome { type m[O] <: UpperBound[O] }]] def high(h :High[m forSome { type m[O] <: UpperBound[O] }

问题 I am having a hard time understanding what this piece of code does exactly: import scala.language.implicitConversions implicit def list2ordered[A](x: List[A]) (implicit elem2ordered: A => Ordered[A]): Ordered[List[A]] = new Ordered[List[A]] { //replace with a more useful implementation def compare(that: List[A]): Int = 1 } It comes from the Scala Tour and it is in the section "Implicit Conversions". I understand that list2ordered takes a List[A] that comes from the left hand side of List(1, 2

问题 I am having a hard time understanding what this piece of code does exactly: import scala.language.implicitConversions implicit def list2ordered[A](x: List[A]) (implicit elem2ordered: A => Ordered[A]): Ordered[List[A]] = new Ordered[List[A]] { //replace with a more useful implementation def compare(that: List[A]): Int = 1 } It comes from the Scala Tour and it is in the section "Implicit Conversions". I understand that list2ordered takes a List[A] that comes from the left hand side of List(1, 2