前向参考扩展了价值问题的定义 [英] Forward reference extends over definition of value problem

问题描述

我在 Scala 中遇到了一些问题来解决隐式值，并且我在 netbeans 中有一个神秘的错误消息:

i have some problem in scala to resolve implicit values, and i have the cryptic error message in netbeans :

错误:前向引用扩展了值的定义......"

"error : Forward reference extends over definition of value ..."

或在 Scala 控制台中，我有其他错误消息

or in the scala console i have an other error message

"类型不匹配:29:错误:类型不匹配；找到:Factory.type(具有基础类型对象工厂)需要:通用工厂"

"type mistmatch :29: error: type mismatch; found : Factory.type (with underlying type object Factory) required: GenericFactory"

对我的类和主要功能的一些描述:

Some description of my class and main function :

import java.util.Random

//////////
// Main //

//Implicit random for all classes and object
implicit val aprng = new Random

//Implicit object Factory used in other class
implicit val factory = Factory

abstract class GenericFactory {
def build 
}

object Factory extends GenericFactory{
def build = println("return factory")
}

class A (rate: Random => Double = aprng => aprng.nextFloat, val factory : GenericFactory) {

  def this(rate : Double, factory : GenericFactory) = this( _ => rate, factory)

  def operate(genomes: IndexedSeq[Int])(implicit aprng: Random) = { 
println("calculate genomes with aprng random values")}
}

object B{
val instanceOfA = new A(rate => 0.5d,factory)
}

我有两个问题，因为 1) 我可以在 A 类的参数中传递一个对象，所以我定义了一个抽象类来传递这个抽象类，但这在这里不起作用:/2) 之后，我定义到 A 类中的隐式值无法识别，并失败并显示错误消息.

I have 2 problem because 1) i can pass an object in argument of class A, so i define an abstract class to pass this abstract class, but that not work here :/ 2) After that, my implicit value defined into class A is not recognized, and fail with error message.

您有解决此问题的想法或答案吗?

Do you have an idea or an answer to resolve this problem ?

我在 agisteel 的帮助下更新了代码，没关系，代码正在运行 :)

I update the code with help of agisteel, it's ok, code running :)

import java.util.Random

//////////
// Main //

//Implicit random for all classes and object
implicit val aprng = new Random
implicit val function: Random => Double = arpng => arpng.nextFloat

abstract class GenericFactory 
{
  def build = println("build")
}

implicit object Factory extends GenericFactory
{
  def build = println("return factory")
}

class A (implicit rate: Random => Double, implicit val factory : GenericFactory) {

  //def this(rate : Double, factory : GenericFactory) = this( _ => rate, factory)

  def operate(genomes: IndexedSeq[Int])(implicit aprng: Random) = { 
    println("calculate genomes with aprng random values")}
}

object B{
val instanceOfA = new A
}

推荐答案

我不确定你在这里想要达到什么目的，但这里有一些提示:

I'm not sure what you are trying to achieve here, but here are few tips:

1) 而不是:

implicit val factory = Factory
object Factory extends GenericFactory { ...

试试这个:

implicit object Factory extends GenericFactory { ...

2) 据我所知，lambda 的默认值只能通过隐式提供，而不是:

2) Default values for lambdas can only be provided via implicits as far as I know, so instead of:

class A (rate: Random => Double = aprng => aprng.nextFloat, ...

试试这个:

implicit val function: Random => Double = arpng => arpng.nextFloat
class A (implicit rate: Random => Double) ( ...

我希望这些信息有用.

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