[英]Scala: How to simplify nested pattern matching statements
我正在Scala中编写一个Hive UDF(因为我想学习scala)。 为此,我必须覆盖三个函数: evaluate
, initialize
和getDisplayString
。
在初始化函数中,我必须:
ObjectInspector
数组并返回ObjectInspector
为此,我使用模式匹配并提出以下功能:
override def initialize(genericInspectors: Array[ObjectInspector]): ObjectInspector = genericInspectors match {
case null => throw new UDFArgumentException(functionNameString + ": ObjectInspector is null!")
case _ if genericInspectors.length != 1 => throw new UDFArgumentException(functionNameString + ": requires exactly one argument.")
case _ => {
listInspector = genericInspectors(0) match {
case concreteInspector: ListObjectInspector => concreteInspector
case _ => throw new UDFArgumentException(functionNameString + ": requires an input array.")
}
PrimitiveObjectInspectorFactory.getPrimitiveWritableObjectInspector(listInspector.getListElementObjectInspector.asInstanceOf[PrimitiveObjectInspector].getPrimitiveCategory)
}
}
尽管如此,我的印象是函数可以变得更清晰,并且通常更漂亮,因为我不喜欢有太多缩进级别的代码。
是否有一种惯用的Scala方法来改进上面的代码?
模式通常包含其他模式。 这里的x
的类型是String。
scala> val xs: Array[Any] = Array("x")
xs: Array[Any] = Array(x)
scala> xs match {
| case null => ???
| case Array(x: String) => x
| case _ => ???
| }
res0: String = x
“任意数量的args”的习语是“序列模式”,它匹配任意args:
scala> val xs: Array[Any] = Array("x")
xs: Array[Any] = Array(x)
scala> xs match { case Array(x: String) => x case Array(_*) => ??? }
res2: String = x
scala> val xs: Array[Any] = Array(42)
xs: Array[Any] = Array(42)
scala> xs match { case Array(x: String) => x case Array(_*) => ??? }
scala.NotImplementedError: an implementation is missing
at scala.Predef$.$qmark$qmark$qmark(Predef.scala:230)
... 32 elided
scala> Array("x","y") match { case Array(x: String) => x case Array(_*) => ??? }
scala.NotImplementedError: an implementation is missing
at scala.Predef$.$qmark$qmark$qmark(Predef.scala:230)
... 32 elided
这个答案不应被解释为主张回归类型安全。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.