implicit

问题 I am trying to write code to represent polynomials within Scala. I need this code to be type polymorphic, so I am using implicits to deal with different types. I have: case class Mono[T](degree: Int, coeff: T) { def Degree: Int = return degree def Coeff: T = return coeff } class Poly[T](private val terms: List[Mono[T]]) { trait Semiring[T] { def add(x:T, y:T): T def mul(x:T, y:T): T def exponent(x: T, n:Int): T val unitA: T } implicit object IntSemiring extends Semiring[Int] { def add(x: Int,

问题 Update! See my dissection of a portion of the C# spec below; I think I must be missing something, because to me it looks like the behavior I'm describing in this question actually violates the spec. Update 2! OK, upon further reflection, and based on some comments, I think I now understand what's going on. The words "source type" in the spec refer to the type being converted from -- i.e., Type2 in my example below -- which simply means that the compiler is able to narrow the candidates down

问题 I've been reading some stuff on Scala type level programming. Mainly the Apocalisp blog, and also a youtube talk by Alexander Lehmann. I am a bit stuck on something which I guess is probably very basic, which is the use of implicitly to compare two types as shown below: implicitly[Int =:= Int] Mark on the Apocalisp blog says: This is useful for capturing an implicit value that is in scope and has type T. I get how to make this work, but I don't really know why it works and so don't want to

问题 I've been reading some stuff on Scala type level programming. Mainly the Apocalisp blog, and also a youtube talk by Alexander Lehmann. I am a bit stuck on something which I guess is probably very basic, which is the use of implicitly to compare two types as shown below: implicitly[Int =:= Int] Mark on the Apocalisp blog says: This is useful for capturing an implicit value that is in scope and has type T. I get how to make this work, but I don't really know why it works and so don't want to

问题 Is it possible to define an implicit conversion of enums in c#? something that could achieve this? public enum MyEnum { one = 1, two = 2 } MyEnum number = MyEnum.one; long i = number; If not, why not? For further discussion and ideas on this, I followed up with how I currently handle this: Improving the C# enum 回答1: There is a solution. Consider the following: public sealed class AccountStatus { public static readonly AccountStatus Open = new AccountStatus(1); public static readonly

问题 I am on Linux and gcc 4.2.3. For the below code portion, lp_parm_talloc_string function is called implicitly and afterwards it is defined: char *lp_parm_string(const char *servicename, const char *type, const char *option) { return lp_parm_talloc_string(lp_servicenumber(servicename), type, option, NULL); } /* Return parametric option from a given service. Type is a part of option before ':' */ /* Parametric option has following syntax: 'Type: option = value' */ /* the returned value is

问题 I'm having a little trouble understanding the following phenomenon: trait Trait[A] { def traitType: String } object Trait { implicit val stringTrait: Trait[String] = new Trait[String] { def traitType: String = "string" } implicit val intTrait: Trait[Int] = new Trait[Int] { def traitType: String = "int" } } class Media[A] { // works def mediaType(implicit t: Trait[A]): String = t.traitType // does not compile def mediaType: String = implicitly[Trait[A]].traitType } object Main { def main(args:

问题 I've started getting this strange error; completely not sure what caused it - maybe a Maven rebuild. I can't explain this behavior... sometimes it works in IntelliJ, sometimes it doesn't, and it is failing when I run it from a jar file. This is the runtime error: java.lang.NoSuchMethodError: breeze.linalg.DenseVector$.canScaleD()Lbreeze/linalg/operators/BinaryOp and it occurs in this code: import breeze.linalg._ import breeze.linalg.DenseVector._ var planeNormal = DenseVector.zeros[Double](39

问题 Working with the Play Framework's JSON Library, I'm creating a Format[T] for some class T. val a: JsPath = (JsPath \ "age") val b: Format[Int] = (JsPath \ "age").format[Int] val x: FunctionalBuilder[OFormat]#CanBuild2[Int, String] = ( (JsPath \ "age").format[Int] and (JsPath \ "location").format[String] ) Looking at the explicit types, we see that (in x ) calling Format[Int] and Format[String] returns a type of FunctionalBuilder[OFormat]#CanBuild2[Int, String] . How does this conversion occur

问题 I'm using a type class that requires its types A to have instances of Scalaz's Order[A] . In my use case, A is a Java class--in particular Joda Time's LocalDate . This class has a natural ordering as it implements Comparable . I couldn't find an Order instance for Comparable s in Scalaz itself, so I tried writing one myself: implicit def comparableOrder[A, B] (implicit ev0: <:<[A, B], ev1: <:<[A, Comparable[B]]): Order[A] = new Order[A] { override def order(x: A, y: A): Ordering = Ordering