美元符号在scala中做了什么？

当我阅读火花源代码 here时,我看到像$(a_variable)这样的代码.
这是什么意思？

我在这里复制代码：

final val blockSize: IntParam = new IntParam(this,"blockSize","Block size for stacking input data in matrices. Data is stacked within partitions." +
      " If block size is more than remaining data in a partition then " +
      "it is adjusted to the size of this data. Recommended size is between 10 and 1000",ParamValidators.gt(0))

  /** @group getParam */
  final def getBlockSize: Int = $(blockSize)

解决方法

这不是特殊的Scala语法,它是一个方法名称.在Scala $是一个合法的标识符.该方法从org.apache.spark.ml.param.Param trait继承.

见source.