Type mismatch error with foldLeft method in Scala

Question

I have a method that uses foldLeft in Scala.

def bitSetToByte(b:collection.BitSet, sh:Int=0) = 
  ((0 /: b) {(acc, input) => acc + (1 << (input - sh))}).toByte

The method has two parameters for the anonymous function, so I replaced it with _ by removing formal arguments.

def bitSetToByte(b:collection.BitSet, sh:Int=0) = ((0 /: b) {(_ + (1 << (_ - sh))}).toByte

The issue is that I have type mismatch error message.

What might be wrong?

Answer 1

When interpreting _, the compiler assumes that the anonymous function that the _ corresponds to is enclosed in the nearest set of parentheses (except for (_)). Basically, the compiler interpreted (_ - sh) to be (x => x - sh), then complained because you were passing a function to << when it expected an Int.