Scala => with =

Question

I am trying to understand Spark internals and also new to Scala. I would like to ask the meaning of (index, res) => results(index) = res in this statement in SparkContext.scala:

runJob[T, U](rdd, func, partitions, (index, res) => results(index) = res)

source: SparkContext.scala

The two things that confound me is the usage of the => and = in the same expression, and the grouping/precedence (should it be interpreted with the => first, or = first then => ?).

The usage of => doesn't seem to match any of the usages of => i read online, and it's not clear what = res is doing.

Thanks!

Answer 1

(index, res) => ... means an anonymous function that receives two parameters ( index and res ).

results(index) = res is the body of the function.

What the function does is to assign res to results on the index position.