为什么Scala枚举在Apache Zeppelin中不起作用，但在Maven中起作用 [英] Why Scala Enumeration does not work in Apache Zeppelin but it works in maven

问题描述

在Maven项目(具有相同的Scala版本)中使用枚举时，枚举可以正常工作.

Enumeration works as expected when I use it in a maven project(with the same Scala version).

object t {
  object DashStyle extends Enumeration {
    val Solid,ShortDash = Value
  }

  def f(style: DashStyle.Value) = println(style)

  def main(args: Array[String]) = f(DashStyle.Solid)
}

但是当它在Apache Zeppelin(Zeppelin 0.6，Spark 1.6，Scala 2.10，Java 1.8)中运行时

But when it runs in Apache Zeppelin(Zeppelin 0.6, Spark 1.6, Scala 2.10, Java 1.8)

object DashStyle extends Enumeration {
    val Solid,ShortDash = Value
}

def f(style: DashStyle.Value) = println(style)

f(DashStyle.Solid) 

即使报告说找到的类型和所需的类型完全相同，它也会报告以下错误

It reports the following error even it says found and required type is exactly the same

<console>:130: error: type mismatch;
 found   : DashStyle.Value
 required: DashStyle.Value
              f(DashStyle.Solid)

为什么以及如何使用它?

Why and how should I use it?

推荐答案

我想出了解决此问题的技巧.

I figured out the trick to solve this issue.

在Apache Zeppelin(或Scala REPL)中.为了使用枚举或密封对象，应将其包装在对象中，但不能直接在根范围上定义.

In Apache Zeppelin (or Scala REPL). In order to use Enumeration or sealed&object, it should be wrapped in object but not directly define on the root scope.

它在maven中起作用的原因是我已经将其放入对象中.

The reason why it works in maven is that I already put it into an object.

在Zeppelin段落中定义对象的枚举

Define enumeration in an object in a Zeppelin paragraph

object t {
  object DashStyle extends Enumeration {
    val Solid,ShortDash = Value
  }

  def f(style: DashStyle.Value) = println(style)
}

然后在Zeppelin段落中使用它

Then use it in a Zeppelin paragraph

import t._
f(DashStyle.Solid)

这篇关于为什么Scala枚举在Apache Zeppelin中不起作用，但在Maven中起作用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！