如何将可以为null或数组的值隐式包装到Scala选项中 [英] How to implicitly wrap a value that can be null or an array into an Scala Option

问题描述

我在Jar文件中包含这个Java类，作为Scala程序的依赖项(例如Axis jar):

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; }
}

在我的Scala程序中，我有一个Java API，可以将MyClass的MyClass实例的实例返回到我在Scala中的程序:

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()

然后，我尝试在我的Scala程序中使用 someStrings 数组，但是它为 null (假设它没有正确初始化)

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(str <- myInstance.getSomeStrings()) ...

因此，这将引发 NullPointerException .

我发现为了在理解中使用它，我可以将其包装到Option中，以便其正确处理NPE.

I've found that in order to use it in the for comprehension I can wrap it into an Option so that it handles the NPE properly.

for(str <- Option[Array[String]](myInstance.getSomeStrings).getOrElse(Array[String]())

但是，对我来说，这看起来并不好.

But that doesn't look OK to me.

有没有一种创建类似隐式方法的方法，即使该方法为空也可以将该值包装到Option中，例如:

Is there a way to create like an implicit method that takes that value even if it's null and wrap it into the Option, like:

implicit def wrapNull(a: Null): Option[Nothing] = None
implicit def wrapArray(a: Array[String]): Option[Array[String]] = Some(a)

所以当我这样做:

for(str <- myInstance.getSomeStrings())

我没有获得 NPE

提前谢谢！

推荐答案

我认为您使用getOrElse的版本没有那么糟糕(您可以通过在Option之后删除[Array[String]]来使其更短一些，因为可以推断出这一点).如果您想要更简洁的方法，可以使用以下方法:

I don't think your version with getOrElse is that bad (you can make it a little shorter by removing the [Array[String]] after Option, since that can be inferred). If you want something even more concise, the following works:

for (str <- Option(myInstance.getSomeStrings).flatten) ...

您还可以使用Option具有foreach的事实:

You could also use the fact that Option has a foreach:

for {
  strings <- Option(myInstance.getSomeStrings)
  str <- strings
} ...

请注意，此处不能使用yield，原因是drexin在下面的注释中突出显示.

Note that you can't use yield here, for the reason that drexin highlights in a comment below.

或者您可以皮条客 MyClass:

implicit def withNullWrapper(c: MyClass) = new {
  def getSomeStringsOrNot() = Option(c.getSomeStrings).getOrElse(Array[String]())
}

for (str <- myInstance.getSomeStringsOrNot) ...

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