implicit

问题 I made codes using play framework in scala which look like the following: object Application extends Controller { def hoge = Action( implicit request => val username = MyCookie.getName.get Ok("hello " + username) } } object MyCookie { def getName( implicit request: RequestHeader ) = { request.cookies.get("name").map(_.value) } } I got a code review from my coworker. He said this code is not readable because of implicit parameter. I couldn't reply to his opinion. So could you tell me what is

问题 I am trying to write a generic weighted average function. I want to relax the requirements on the values and the weights being of the same type. ie, I want to support sequences of say: (value:Float,weight:Int) and (value:Int,weight:Float) arguments and not just: (value:Int,weight:Int) To do so, I first need to implement a function that takes two generic numerical values and returns their product. def times[A: Numeric, B: Numeric](x: B, y: A): (A, B) : ??? = {...} Writing the signature and

问题 I am trying to write a generic weighted average function. I want to relax the requirements on the values and the weights being of the same type. ie, I want to support sequences of say: (value:Float,weight:Int) and (value:Int,weight:Float) arguments and not just: (value:Int,weight:Int) To do so, I first need to implement a function that takes two generic numerical values and returns their product. def times[A: Numeric, B: Numeric](x: B, y: A): (A, B) : ??? = {...} Writing the signature and

问题 Consider the following code: object foo { trait Bar[Q[_]] implicit object OptionBar extends Bar[Option] def test[T, C[_]](c: C[T])(implicit bar: Bar[C]) = () def main(args: Array[String]) { test(Some(42): Option[Int]) //??? } } This works, but I need to type the Some(42) as Option[Int], else the implicit object OptionBar won't be resolved (because a Bar[Some] is expected instead). Is there a way to avoid the explicit typing, so that I get the implicit OptionBar object in test even if I feed

问题 Find root of implicit function in Mathematica I have an implicit function, for example: f(x,y) = x^3 + x*y + y^2 - 36 I want to find the root, ie solutions to the equation f(x,y) = 0 Drawing the solution is easy: ContourPlot[x^3 + x*y + y^2 - 36 == 0, {x, -2 Pi, 2 Pi}, {y, -3 Pi, 3 Pi}] however I would like to have the data that is in the plot and not only the visual plot. So how do I find the data of the plot? 回答1: I'm not sure if I am interpreting your second question properly, but assuming

问题 I try to implement some number type and I hit the issue that mynum * 1 works, but not 1 * mynum I tried to define an implicit conversion like this case class Num(v: Int) { def * (o: Int) = new Num(v*o) } implicit def int2Num(v: Int) = Num(v) but it doesn't seem work, because I always get the following error: scala> 1 * new Num(2) <console>:14: error: overloaded method value * with alternatives: (x: Double)Double <and> (x: Float)Float <and> (x: Long)Long <and> (x: Int)Int <and> (x: Char)Int

问题 Please refer to the source code below. All source code is defined in the same package. When I define all of the code within a single source file ShowMain.scala , I get a compile error, however when object ShowMain is defined in ShowMain.scala and trait Show and object Show are defined in Show.scala , there is no compile error. My question: What is the cause for this? What language rule have I run afoul of? Example code: object ShowMain { def main(args: Array[String]): Unit = { output("hello")

问题 tl;dr : How do I do something like the made up code below: def notFunctor[M[_] : Not[Functor]](m: M[_]) = s"$m is not a functor" The ' Not[Functor] ', being the made up part here. I want it to succeed when the 'm' provided is not a Functor, and fail the compiler otherwise. Solved : skip the rest of the question and go right ahead to the answer below. What I'm trying to accomplish is, roughly speaking, "negative evidence". Pseudo code would look something like so: // type class for obtaining

问题 I am trying to write a text game and I have run into an error in the function I am defining that lets you basically spend your skill points after you make your character. At first, the error stated that I was attempting to subtract a string from an integer in this part of the code: balance - strength . Obviously that was wrong so I fixed it with strength = int(strength) ... but now I am getting this error which I have never seen before(new programmer) and I am stumped on what exactly it is

问题 I am trying to write a text game and I have run into an error in the function I am defining that lets you basically spend your skill points after you make your character. At first, the error stated that I was attempting to subtract a string from an integer in this part of the code: balance - strength . Obviously that was wrong so I fixed it with strength = int(strength) ... but now I am getting this error which I have never seen before(new programmer) and I am stumped on what exactly it is