scala-2.10

问题 What's the best practice for calling a constructor of a class in scala 2.10 (M4+) ? 回答1: Answering my own question: Calling the constructor is different than invoking a method. Here's the right way to do it in scala 2.10 import reflect.runtime.universe._ import reflect.runtime.currentMirror val typ = typeOf[Range] val constructor = typ.members.find(_.kind == "constructor").get.asMethodSymbol currentMirror reflectClass typ.typeSymbol.asClassSymbol reflectConstructor constructor apply (1,10,1)

问题 Scala does not provide chained comparisons as Python does: // Python: 0 < x <= 3 // Scala: 0 < x && x <= 3 Will Scala 2.10 with the new macro feature enable the programmer write a library that adds this feature? Or is this beyond the scope of Scala's macros? Macros seem to be the right choice for the implementation of such syntactic sugar as they do not complicate the parser/compiler. 回答1: You don't need macros for it: class ChainedComparisons[T : Ordering](val res: Boolean, right: T) { def <

问题 I'm attempting to write a macro that would wrap a function and deducting a parameter from the value its invocation will be assigned to. object TestMacros { def foo(name: String): String = name.toUpper def bar = macro barImpl def barImpl(c: Context): c.Expr[String] = { import c.universe._ //TODO extract value name (should be baz) c.Expr[String](Apply( Select(newTermName("TestMacros"), newTermName("foo")), // Probably wrong, just typed it quickly for demonstration purposes List(Literal(Constant

问题 How can I access the name of the code file and line number in a Scala macro? I looked at SIP-19 and it says it can be easily implemented using macros... EDIT: To clarify, I want the code file and line number of the caller. I already have a debug macro and I want to modify it to print the line number and file name of whoever calls debug 回答1: You want c.macroApplication.pos , where c is for Context . c.enclosingPosition finds the nearest macro on the stack that has a position. (See the other

问题 I would like to have a scala macro that does the following: When I write: myCreateCityMacro("paris") myCreateCityMacro("vallorbe") I would like to get: val paris = new City("paris") val vallorbe = new City("vallorbe") 回答1: This can be solved using scala Dynamic feature: import scala.language.dynamics object Cities extends App { var c = new DynamicMap[String, City]() createCity("Paris") createCity("Vallorbe") println(c.Paris, c.Vallorbe) def createCity(name: String) { c.self.update(name, new

问题 How do I do something like this in Scala? case class Foo[A](x: A) { def get[T]: Option[T] = x match { case x: T => Some(x) // if x is of type T i.e. T =:= A case _ => None } } val test = Foo("hi") assert(test.get[Int] == None) assert(test.get[String] == Some("hi")) I tried this and ran into some weird time inference failure: import scala.util.{Try, Success} import reflect._ case class Foo[A](x: A) extends Dynamic { def get[T: ClassTag]: Option[T] = Try(x.asInstanceOf[T]) match { case Success

问题 Is there a way the file name of the current file (when the code is written) in scala? Like my class is in a file like com/mysite/app/myclass.scala and i want to call a method that will return "myclass.scala" (or the full path...) Thank you! 回答1: This can be achieved with Scala macros, an experimental language feature available from version 2.10. Macros make it possible to interact with the building of the AST during the source code parsing phase, and to modify trees of AST before the actual

问题 This code compiles with Scala 2.9.2: trait HK { type Rep[A] def unzip1[A, B, C[_]](ps: Rep[C[(A, B)]]): (Rep[C[A]], Rep[C[B]]) def doUnzip1[A, B](ps: Rep[List[(A, B)]]) = unzip1(ps) } But with Scala 2.10.0 it doesn't compile with the following error (higherKinded language feature is enabled): [info] Compiling 1 Scala source to /home/klyuchnikov/code/hk/target/scala-2.10/classes... [error] /home/klyuchnikov/code/hk/src/main/scala/HK.scala:6: type mismatch; [error] found : HK.this.Rep[List[(A,

问题 I'm running into a weird issue with reflection in Scala 2.10.0 Milestone 4 that I can't wrap my head around. First for the stuff that works the way I'd expect: scala> import scala.reflect.runtime.universe._ import scala.reflect.runtime.universe._ scala> trait A[X]; trait B[Y] extends A[Y] defined trait A defined trait B scala> typeOf[B[String]].parents res0: List[reflect.runtime.universe.Type] = List(java.lang.Object, A[String]) scala> typeOf[B[String]].parents contains typeOf[A[String]] res1

问题 I am trying to unit test an upload call but I get this error for the following code: @MultipartConfig(maxFileSize = 3145728) class WebServlet extends ScalatraServlet with FileUploadSupport { override def isSizeConstraintException(e: Exception) = e match { case se: ServletException if se.getMessage.contains("exceeds max filesize") || se.getMessage.startsWith("Request exceeds maxRequestSize") => true case _ => false } error { case e: SizeConstraintExceededException => RequestEntityTooLarge("too