implicit

问题 Preserved question - see Edit at the bottom I'm working on a small functional library, basically to provide some readability by hiding basic cyclomatic complexities. The provider is called Select<T> (with a helper factory called Select ), and usage is similar to public Guid? GetPropertyId(...) { return Select .Either(TryToGetTheId(...)) .Or(TrySomethingElseToGetTheId(...)) .Or(IGuessWeCanTryThisTooIfWeReallyHaveTo(...)) //etc. ; } and the library will take care of the short circuiting, etc. I

问题 I have a function with the following signature: myFunc[T <: AnyRef](arg: T)(implicit m: Manifest[T]) = ??? How can I invoke this function if I do not know the exact type of the argument at the compile time? For example: val obj: AnyRef = new Foo() // At compile time obj is defined as AnyRef, val objClass = obj.getClass // At runtime I can figure out that it is actually Foo // Now I would need to call `myFunc[Foo](obj.asInstanceOf[Foo])`, // but how would I do it without putting [Foo] in the

问题 Why iWantInt(a) does not compile while iWantInt(b) and - what is more surprising - iWantInt does ? How can I understand this behaviour ? Why can I not pass explicitly a to iWantInt when I can pass it implicitly ? How is iWantA different from iWantInt ? Why does it not work the same way ? Is this behavior documented/explained somewhere ? If Scala would accept iWantInt(a) what kind of problems would that cause ? Why is it forbidden ? class A class B object Run extends App { implicit val a = new

问题 I would like to apply a function to all objects in a list, where all objects in the list inherit from a common class. In this function, I would like to use an implicit class to ensure that the correct operation is applied based on the object's type. For example, I want to ensure that all Employee objects in a list are converted using the employeeConverter below. Calling convert with the Employee directly works just fine, but applying convert to a list of Employee objects is a compiler error.

问题 In following code from Scala's puzzlers, it seems that there is no conflict in implicits because TestAlarmHandler is more specific. I didn't understand the explanation though. Why is TestAlarmHandler is more specific than DefaultAlarmHandler ? object Scanner { trait Console { def display(item: String) } trait AlarmHandler extends (() => Unit) def scanItem(item: String)(implicit c: Console) { c.display(item) } def hitAlarmButton()(implicit ah: AlarmHandler) { ah() } } class OperatingMode {

问题 In the following code , implicit typecasting for an integer value 9 take place and assigned to variable of byte datatype which is of size 8 bits. class Demo1 { public static void main(String args[]) { byte b=9; System.out.println(b); } } The code happily compiled and executed . but when i wrote the following code it gave me compilation error class Demo2 { void func1(byte b) { System.out.println(b); } public static void main(String[] args) { Demo2 d1=new Demo2(); d1.func1(9); } } please

问题 I'm migrating a jsf 2.0 application to jsf 2.2.6. There is a extensive use of implicit EL object component as styleClass="#{component.valid?'':'err'}". In jsf 2.2.6 (jsf-impl-2.2.6-jbossorg-4.jar) valid is not recognized, throwing "ServletException: The class 'javax.faces.component.html.xxx' does not have the property 'valid". Is this functionality deprecated in jsf 2.x.x? Can be related to JBoss EL? 回答1: It seems that you trying the component.valid on element that does not support it at all,

问题 I'm working with Slick's GetResult typeclass and wanted to use Shapeless to derive instances of GetResult[Option[(A, B, C...)]] What I want: Given an implicit GetResult[Option[A]], GetResult[Option[B]], ... , implicitly generate a GetResult[Option[(A, B, ...)]] What I tried trait CanGetOption[T] { def getOption: GetResult[Option[T]] } object CanGetOption { // convenience implicit resolver def apply[T](implicit canGetOption: CanGetOption[T]): CanGetOption[T] = canGetOption // base case: HNil

问题 Let's say that I have two particular object 's from which I retrieve imports. Assume that both objects have multiple, useful imports that I want to use. I'm only including 1 for simplicity of this example: scala> object Implicits1 { implicit def good: String => Int = _ => 42 } defined object Implicits1 scala> object Implicits2 { implicit def bad: String => Int = _ => 666 } defined object Implicits2 Then, given foo : scala> def foo(x: Int): Int = x foo: (x: Int)Int I perform my wildcard

问题 I'm currently converting and casting from Class to Class2 using the implicit operator. But what I want to do is, that, whenever I refer to foo (Class<Class2>) , I'd like for Goo(Class) to be returned so that I can access the public Properties of it directly, without having to cast it first into a new variable. In other words, I want that when I access Class<Class> , I'd like Goo to be returned. I'm aware I might have not been able to explain properly so feel free to ask in the comment section