Missing parameter type for expanded function in Scala ArrayBuffer
parameters, scala, sorting, types
Solution
`.sorted` takes an implicit parameter of type `Ordering` (similar to Java `Comparator`). For integers, the compiler will provide the correct instance for you:
scala> b.sorted
res0: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 2, 7, 9)
If you want to pass a comparison function, use `sortWith`:
scala> b.sortWith( _ < _ )
res2: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 2, 7, 9)
scala> b.sortWith( _ > _ )
res3: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(9, 7, 2, 1)
However, pay attention, although `ArrayBuffer` is mutable, both sort methods will return a copy which is sorted, but the original won't be touched.
Problem
While trying to run the following snippet from Scala for the impatient: ``` val b = ArrayBuffer(1,7,2,9) val bSorted = b.sorted(_ < _) ``` I get the following error: ``` error: missing parameter type for expanded function ((x$1, x$2) => x$1.$less(x$2)) val bSorted = b.sorted(_ < _) ``` Can somebody explain what might be going on here. Shouldn't the parameter type be inferred from the contents of the ArrayBuffer or do I need to specify it explicitly? Thanks