Add BitSet union iterator (#308)

Author: regadas

core/js/src/main/scala/cats/parse/BitSet.scala

@@ -46,11 +46,14 @@ object BitSetUtil {
 
   def isSingleton(t: Tpe): Boolean = t.size == 1
 
+  def union(bs: List[(Int, BitSet)]): Iterable[Char] =
+    union(bs.iterator)
+
   // what are all the Chars in these bitsets
-  def union(bs: List[(Int, BitSet)]): Iterable[Char] = {
+  def union(bs: Iterator[(Int, BitSet)]): Iterable[Char] = {
     def toIter(m: Int, bs: BitSet): Iterator[Char] =
       bs.iterator.map { i => (i + m).toChar } ++ Iterator.single(m.toChar)
 
-    bs.iterator.flatMap { case (m, bs) => toIter(m, bs) }.toSet
+    bs.flatMap { case (m, bs) => toIter(m, bs) }.toSet
   }
 }

core/jvm/src/main/scala/cats/parse/BitSet.scala

@@ -49,13 +49,16 @@ object BitSetUtil {
   def isSingleton(t: Tpe): Boolean = t.cardinality() == 1
 
   // what are all the Chars in these bitsets
-  def union(bs: List[(Int, BitSet)]): Iterable[Char] = {
+  def union(bs: List[(Int, BitSet)]): Iterable[Char] =
+    union(bs.iterator)
+
+  def union(bs: Iterator[(Int, BitSet)]): Iterable[Char] = {
     def toIter(m: Int, bs: BitSet): Iterator[Char] =
       Iterator
         .iterate(0) { m => bs.nextSetBit(m + 1) }
         .takeWhile(_ >= 0)
         .map { i => (m + i).toChar }
 
-    bs.iterator.flatMap { case (m, bs) => toIter(m, bs) }.toSet
+    bs.flatMap { case (m, bs) => toIter(m, bs) }.toSet
   }
 }

core/shared/src/main/scala/cats/parse/Parser.scala

@@ -2675,7 +2675,7 @@ object Parser {
             case one :: Nil => Chain.one(one.asInstanceOf[P0])
             case many =>
               // we need to union
-              val minBs: List[(Int, BitSetUtil.Tpe)] = many.map { case CharIn(m, bs, _) => (m, bs) }
+              val minBs = many.iterator.map { case CharIn(m, bs, _) => (m, bs) }
               Chain.one(Parser.charIn(BitSetUtil.union(minBs)).asInstanceOf[P0])
           }
 

core/shared/src/test/scala/cats/parse/BitSetTest.scala

@@ -26,7 +26,7 @@ import org.scalacheck.Prop.forAll
 class BitSetTest extends munit.ScalaCheckSuite {
   property("BitSetUtil union works") {
     forAll { (cs: List[List[Char]]) =>
-      val arys = cs.filter(_.nonEmpty).map(_.toArray.sorted)
+      val arys = cs.iterator.filter(_.nonEmpty).map(_.toArray.sorted)
       val bs = arys.map { ary => (ary(0).toInt, BitSetUtil.bitSetFor(ary)) }
       val sortedFlat = BitSetUtil.union(bs)
       assertEquals(sortedFlat.toSet, cs.flatten.toSet)