implicit

问题 I try to override this method def sum[B >: A](implicit num: Numeric[B]): B = ... in a subclass where type A is already fixed to Int . I already tried override def sum: Int = ... but this doesn't override of course, leading to different method resolution based on the dynamic type at runtime. Going further, def sum[B >: Int](implicit num: Numeric[B]): Int does override, while def sum[B >: Int](implicit num: Numeric[Int]): Int does not, as well as def sum(implicit num: Numeric[Int]): Int Why is

问题 User Régis Jean-Gilles gracefully answered my previous question where I was struggling with CanBuildFrom and enrichment functions (aka "pimp my library" or "enrich my library"): Creating an implicit function that wraps map() in Scala with the right type: Not for the faint at heart But this time I've got an even more complicated issue. I have a function to implement variations on intersectWith , for intersecting collections by their keys. I've managed to make them work like proper collection

问题 It is suggested that whether your app uses code or token as your response_type you should perform an automated check on the access_token to confirm that the token belongs to the person the app expects it to belong to and that it was your app that generated the token. You are supposed to do this on GET graph.facebook.com/debug_token? input_token={token-to-inspect} &access_token={app-token-or-admin-token} where app-token is app_id|app_secret and token-to-inspect is the user's access_token. Also

问题 i have some problem in scala to resolve implicit values, and i have the cryptic error message in netbeans : "error : Forward reference extends over definition of value ..." or in the scala console i have an other error message "type mistmatch :29: error: type mismatch; found : Factory.type (with underlying type object Factory) required: GenericFactory" Some description of my class and main function : import java.util.Random ////////// // Main // //Implicit random for all classes and object

问题 Context object Fibonacci { final val Threshold = 30 def fibonacci(n: Int)(implicit implementation: Fibonacci): Int = implementation match { case f: functional.type if n > Threshold => fibonacci(n)(imperativeWithLoop) case f: imperativeWithRecursion.type => f(n) case f: imperativeWithLoop.type => f(n) case f: functional.type => f(n) } sealed abstract class Fibonacci extends (Int => Int) object functional extends Fibonacci { def apply(n: Int): Int = if (n <= 1) n else apply(n - 1) + apply(n - 2

问题 I have never done any extensive work with overloading operators, especially the implicit and explicit conversions. However, I have several numeric parameters that are used frequently, so I am creating a struct as a wrapper around a numeric type to strongly type these parameters. Here's an example implementation: public struct Parameter { private Byte _value; public Byte Value { get { return _value; } } public Parameter(Byte value) { _value = value; } // other methods (GetHashCode, Equals,

问题 As a follow up to my other question, see comments / questions in code: case class Implicit(name: String) def foo(implicit i: Implicit = null) = println(Option(i)) def bar1(implicit i: Implicit) { foo // prints None implicit val i = Implicit("J") // Why is call to foo above affected although this line comes after? foo // prints Some(Implicit(I)) } def bar2(implicit i: Implicit) { foo // prints None implicit val i = null implicit val j = Implicit("J") foo // prints None // Why? Should raise

问题 I am playing around with Shapeless and I am trying to compute the (kind-of) powerset of an HList of Option s. Basically, I want to interpret the HList as a set, in which case the Option value of an element tells me it belongs to the set or not. For example, given Some(5) :: Some("a") :: HNil , I want to obtain the following HList s: Some(5) :: Some("a") :: HNil Some(5) :: None :: HNil None :: Some("a") :: HNil None :: None :: HNil I tried the following: object test2 extends Poly2{ implicit

问题 trait Eq[-A] { def eq(a: A, b: A): Boolean } object Eq { implicit object IntEq extends Eq[Int] { def eq(a: Int, b: Int) = a == b } } trait Supertrait[+A] object Supertrait { implicit def Eq[A: Eq]: Eq[Supertrait[A]] = ??? } trait Subtrait[+A] extends Supertrait[A] object Subtrait { implicit def Eq[A: Eq]: Eq[Subtrait[A]] = ??? } def f[A](x: Subtrait[A])(implicit ev: Eq[Subtrait[A]]) = ??? f(new Subtrait[Int] {}) When compiling this code, the following error occurs: Error:(32, 4) ambiguous

问题 As it is MyClass x = 120; , is it possible to create such a custom class? If so, how can I do that? 回答1: It's generally considered a bad idea to use implicit operators, as they are, after all, implicit and run behind your back. Debugging code littered with operator overloads is a nightmare. That said, with something like this: public class Complex { public int Real { get; set; } public int Imaginary { get; set; } public static implicit operator Complex(int value) { Complex x = new Complex();