implicit

问题 I'd like to use GNU make to automate batch file processing, in my particular case I have a huge number of image files, I'd like to colorspace convert and reencode them to a custom file format. The file format encoder accepts only filenames on the command line, i.e. no stdio redirection. My file and directory structure is ./sourceimages/*.tif ./destimages/*.mie ./Makefile I wrote a peliminary Makefile with a pattern rule %.mie : %.tif tmpraw := $(shell mktemp --suffix=raw) convert $<

问题 I have the following (simplified) code: case class Value[T](value: T) trait Absable[In,Out] { def absoluteValue(in: In): Out } implicit class AbsValue[In, Out](in: Value[In]) { def abs()(implicit ev: Absable[In, Out]): Value[Out] = Value(ev.absoluteValue(in.value)) } implicit def AbsNumeric[A : Numeric] = new Absable[A, A] { def absoluteValue(in: A) = implicitly[Numeric[A]].abs(in) } Now I want to use the abs function on a Value : scala> Value(-3).abs() res3: Value[Int] = Value(3) scala>

问题 Given the following object with 2 implicits: scala> object Foo { | implicit def stringToInt(x: String) = 555 | implicit def stringToBoolean(x: String) = true | } warning: there were two feature warnings; re-run with -feature for details defined object Foo I can use them: scala> def f(x: Int) = x f: (x: Int)Int scala> import Foo._ import Foo._ scala> f("asdf") res0: Int = 555 scala> def g(b: Boolean) = b g: (b: Boolean)Boolean scala> g("asdfasdf") res1: Boolean = true Then, I tried to disable

问题 The following code gives an error: package test trait Base { def method:String } trait Trait extends Base { def method()(implicit i:String):String = { "2" } } object Object extends Trait { } The error is "object creation impossible, since method method in class Base of type => String is not defined" The above error is fixed by following code package test trait Base { def method:String } trait Trait extends Base { def method:String = method()("String") // Over loading def method()(implicit i

问题 The following code gives an error: package test trait Base { def method:String } trait Trait extends Base { def method()(implicit i:String):String = { "2" } } object Object extends Trait { } The error is "object creation impossible, since method method in class Base of type => String is not defined" The above error is fixed by following code package test trait Base { def method:String } trait Trait extends Base { def method:String = method()("String") // Over loading def method()(implicit i

问题 I've got a problem with implicit casting, templates and inheritance from template classes. The following is what I extracted from my project, I have left out that some classes are even abstract, but it does not have to do with the case. class A {}; class B : public A {}; template <typename T> class Base {}; class Derived : public Base<B> {}; int main() { Derived d; Base<A>* base = new Derived(); } Basically, I have a template base class Base that I derive Derived : public Base<B> from. Then I

问题 I have this Java class in a Jar file included as a dependency of an Scala program (like the Axis jar): class MyClass { private String[] someStrings; public String[] getSomeStrings() { return someStrings; } } In my Scala program I have a Java API that return an instance of MyClass instance of MyClass to my program in Scala: val myInstance = JavaAPI.getInstanceOfMyClass() Then I try to use the someStrings array in my Scala program but it's null (let say that it wasn't properly initialized) for

问题 Apparently unapply/unapplySeq in extractor objects do not support implicit parameters. Assuming here an interesting parameter a, and a disturbingly ubiquitous parameter b that would be nice to hide away, when extracting c. [ EDIT ]: It appears something was broken in my intellij/scala-plugin installation that caused this. I cannot explain. I was having numerous strange problems with my intellij lately. After reinstalling, I can no longer reprodce my problem. Confirmed that unapply/unapplySeq

问题 Consider the following code: class A { def print = println("A") } class B extends A { override def print = println("B") } def foo(implicit a: A) = a.print def bar(implicit a: A) = { implicit val b = new B foo } bar(new A) // B I am wondering why calling foo in bar isn't raising an ambiguous implicit values error. Of course implicit val b: A = new B will raise that error. Why does foo pick the implicit b and not the implicit a ? Or even more general: What are the rules what will be picked?

问题 I'm trying to create a implicit conversion of Scala's Function1 to java.util.function.Function. Here's my code: object Java8ToScala extends App { implicit def javaFuncToScalaFunc[T, R](func1: Function[T, R]): function.Function[T,R] = { new function.Function[T, R] { override def apply(t: T): R = func1.apply(t) } } val javaFunc:function.Function[String,Int] = (s:String) => s.length println(javaFunc.apply("foo")) // this works private val strings = new util.ArrayList[String]() println(strings