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scalaapache-spark-ml

How does $(objectName) work in Scala Spark?

Hi I am trying to learn org.apache.spark.ml design. I noticed in that param values are often retrieved by using $ symbol. For example, in NGram.scala 

val n: IntParam = new IntParam(this, "n", "number elements per n-gram (>=1)", 
  ParamValidators.gtEq(1))

/** @group setParam */
def setN(value: Int): this.type = set(n, value)

/** @group getParam */
def getN: Int = $(n)

Is $ a Scala operator with general features?

I can see in eclipse (when I hoverover $(n)) that it is defined as

final protected def $[T](param: Param[T]): T

but I could not find the class where it was defined the above way.

Can you please tell me where this is defined ?

Solution

  • A dollar sign is a perfectly legal method name in Scala. You can see the definition of this method here.

    In this case, it is simply an alias for getOrDefault.