scala-2.10

问题 Following up on this question, I'm trying to figure out how to call a method on an object. The relevant definitions are: trait ThirdParty { def invoke = println("right") } trait WeatherIcon { def invoke = println("wrong") } class MyClass { object objA extends ThirdParty object objB extends WeatherIcon } I got a Symbol for objA like this: import reflect.runtime.universe._ val stuff = typeOf[MyClass].members.filter(_.isValue).filter(_.typeSignature <:< typeOf[ThirdParty]) That returns an

问题 I've been fighting with this for hours and I can't figure out why after deploying my Scala Play 2.2 application in Heroku I get this stacktrace: 2013-09-30T01:05:09.413177+00:00 heroku[web.1]: Starting process with command `target/start -Dhttp.port=18174 $PLAY_OPTS` 2013-09-30T01:05:10.931893+00:00 app[web.1]: bash: target/start: No such file or directory 2013-09-30T01:05:12.382399+00:00 heroku[web.1]: Process exited with status 127 2013-09-30T01:05:12.414050+00:00 heroku[web.1]: State

问题 I am confused by the following behavior - why does reducing an Array of Int work using math.max, but an Array of Float requires a wrapped function? I have memories that this was not an issue in 2.9, but I'm not completely certain about that. $ scala -version Scala code runner version 2.10.2 -- Copyright 2002-2013, LAMP/EPFL $ scala scala> import scala.math._ scala> Array(1, 2, 4).reduce(max) res47: Int = 4 scala> Array(1f, 3f, 4f).reduce(max) <console>:12: error: type mismatch; found : (Int,

问题 I'm trying to call the Selenium Java libraries from Scala. I'm using Scala IDE (Eclipse), and Scala 2.10.2. What is causing this compiler error? error while loading Function, class file '/Dev/selenium-2.35.0/libs/guava- 14.0.jar(com/google/common/base/Function.class)' is broken (class java.lang.RuntimeException/bad constant pool index: 0 at pos: 479) Sometimes I fix broken class file errors by including more jars -- jars that javac would not need to see, but apparently scalac does. But is

问题 I am writing a macro in Scala, but when I call it I get an error message saying "Double does not take parameters". Clearly there is something wrong with how the macro builds the AST. So how can I see the expanded macro? Is there a way to call the macro implementation at runtime? 回答1: Provide -Ymacro-debug-lite or -Ymacro-debug-verbose option to the compiler. Off the top of my head, detalization of printed ASTs is governed by -Yshow-trees-compact , -Yshow-trees-stringified , -Xprint-types ,

问题 In Play 2.3, I have a case class with a single optional double member: case class SomeClass(foo: Option[Double]) I need a JSON write converter that handles the member as nullable: implicit val someClassWrite: Writes[SomeClass] = ??? The Play docs provide an example: case class DisplayName(name:String) implicit val displayNameWrite: Writes[DisplayName] = Writes { (displayName: DisplayName) => JsString(displayName.name) } But sadly I can't figure out how to do this for 1) a single nullable and

问题 This question already has an answer here : Closed 6 years ago . Possible Duplicate: Scala 2.10: What is a TypeTag and how do I use it? I have been reading about the new TypeTags which come along with the new reflection api. It seems that Manifests are supposed to be replaced with that new concept. Can anyone post some code examples to show the benefits? Some references: TypeTags API SIP: Self-cleaning macros Metaprogramming in Scala 回答1: Manifests are a lie. It has no knowledge of variance

问题 In the following session with scala 2.10.0-M7: scala> trait A defined trait A scala> class B extends A defined class B scala> class C extends A defined class C scala> Some(0).fold(new B){_=>new C} <console>:11: error: type mismatch; found : C required: B Some(0).fold(new B){_=>new C} I would expect the compiler find the common supertype (namely A) rather than complaining. Is it the general type inference limitation, or the consequence of the way Option.fold is defined? Thank you. 回答1: The

问题 I want to do something like this: def assuming[A](condition: => Boolean)(f: => A): A = { require(condition, /* print source-code of condition */) f } Sample usage: def fib(n: Int) = n match { // yes, yes, I know this is not efficient case 0 => 0 case 1 => 1 case i => assuming(i > 0) { fib(i-1) + fib(i-2) } } Now, for example, if you call fib(-20) , I want it to throw an exception with a message like Assertion failed: -20 > 0 or Assertation failed: i > 0 回答1: Dude, isn't an assert macro one of

问题 I want to do something like this: def assuming[A](condition: => Boolean)(f: => A): A = { require(condition, /* print source-code of condition */) f } Sample usage: def fib(n: Int) = n match { // yes, yes, I know this is not efficient case 0 => 0 case 1 => 1 case i => assuming(i > 0) { fib(i-1) + fib(i-2) } } Now, for example, if you call fib(-20) , I want it to throw an exception with a message like Assertion failed: -20 > 0 or Assertation failed: i > 0 回答1: Dude, isn't an assert macro one of