Give separatorCount the more accurate name splitCount.

When omitting empty subsequences, we may skip over multiple adjacent separators, so that
property wasn't counting separators in that case. It's really counting splits.

Author: toddthomas

Sources/Algorithms/LazySplitCollection.swift

@@ -39,7 +39,7 @@ public struct LazySplitCollection<Base: Collection> {
     self._endIndex = Index(
       baseRange: base.endIndex..<base.endIndex,
       sequenceLength: Int.max,
-      separatorCount: Int.max
+      splitCount: Int.max
     )
 
     /// We precalculate `startIndex`. There are three possibilities:
@@ -48,7 +48,7 @@ public struct LazySplitCollection<Base: Collection> {
     self._startIndex = Index(
       baseRange: base.startIndex..<base.startIndex,
       sequenceLength: 1,
-      separatorCount: 0
+      splitCount: 0
     )
     if base.isEmpty {
       if omittingEmptySubsequences {
@@ -61,7 +61,7 @@ public struct LazySplitCollection<Base: Collection> {
       _startIndex = indexForSubsequence(
         atOrAfter: base.startIndex,
         sequenceLength: 0,
-        separatorCount: 0
+        splitCount: 0
       )
     }
   }
@@ -75,16 +75,16 @@ extension LazySplitCollection: LazyCollectionProtocol {
     /// The number of subsequences up to and including this position in the
     /// collection.
     internal let sequenceLength: Int
-    internal let separatorCount: Int
+    internal let splitCount: Int
 
     internal init(
       baseRange: Range<Base.Index>,
       sequenceLength: Int,
-      separatorCount: Int
+      splitCount: Int
     ) {
       self.baseRange = baseRange
       self.sequenceLength = sequenceLength
-      self.separatorCount = separatorCount
+      self.splitCount = splitCount
     }
 
     public static func == (lhs: Index, rhs: Index) -> Bool {
@@ -102,18 +102,15 @@ extension LazySplitCollection: LazyCollectionProtocol {
   internal func indexForSubsequence(
     atOrAfter lowerBound: Base.Index,
     sequenceLength: Int,
-    separatorCount: Int
+    splitCount: Int
   ) -> Index {
-    var newSeparatorCount = separatorCount
     var start = lowerBound
     // If we don't have any more splits to do (which we'll determine shortly),
-    // the end of the next subsequence will be the end of the base collection.
+    // the end of this subsequence will be the end of the base collection.
     var end = base.endIndex
 
-    // The number of separators encountered thus far is identical to the number
-    // of splits performed thus far.
-    if newSeparatorCount < maxSplits {
-      // The non-inclusive end of the next subsequence is marked by the next
+    if splitCount < maxSplits {
+      // The non-inclusive end of this subsequence is marked by the next
       // separator, or the end of the base collection.
       end =
         base[start...].firstIndex(where: isSeparator)
@@ -134,14 +131,18 @@ extension LazySplitCollection: LazyCollectionProtocol {
       }
     }
 
+    var updatedSplitCount = splitCount
     if end < base.endIndex {
-      newSeparatorCount += 1
+      // This subsequence ends on a separator (and perhaps includes other
+      // separators, if we're omitting empty subsequences), so we've performed
+      // another split.
+      updatedSplitCount += 1
     }
 
     return Index(
       baseRange: start..<end,
       sequenceLength: sequenceLength + 1,
-      separatorCount: newSeparatorCount
+      splitCount: updatedSplitCount
     )
   }
 
@@ -166,7 +167,7 @@ extension LazySplitCollection: LazyCollectionProtocol {
 
     guard subsequenceStart != base.endIndex else {
       if !omittingEmptySubsequences
-        && i.sequenceLength < i.separatorCount + 1
+        && i.sequenceLength < i.splitCount + 1
       {
         /// The base collection ended with a separator, so we need to emit one
         /// more empty subsequence. This one differs from `endIndex` in its
@@ -175,7 +176,7 @@ extension LazySplitCollection: LazyCollectionProtocol {
         return Index(
           baseRange: base.endIndex..<base.endIndex,
           sequenceLength: i.sequenceLength + 1,
-          separatorCount: i.separatorCount
+          splitCount: i.splitCount
         )
       } else {
         return endIndex
@@ -185,7 +186,7 @@ extension LazySplitCollection: LazyCollectionProtocol {
     return indexForSubsequence(
       atOrAfter: subsequenceStart,
       sequenceLength: i.sequenceLength,
-      separatorCount: i.separatorCount
+      splitCount: i.splitCount
     )
   }