Replace some C-style forloop with equivalent logic

Author: dduan

stdlib/public/core/CString.swift

@@ -60,7 +60,7 @@ public func _persistCString(s: UnsafePointer<CChar>) -> [CChar]? {
   }
   let length = Int(_swift_stdlib_strlen(s))
   var result = [CChar](count: length + 1, repeatedValue: 0)
-  for var i = 0; i < length; ++i {
+  for i in 0..<length {
     // FIXME: this will not compile on platforms where 'CChar' is unsigned.
     result[i] = s[i]
   }

stdlib/public/core/Character.swift

@@ -120,7 +120,7 @@ public struct Character :
   @warn_unused_result
   static func _smallSize(value: UInt64) -> Int {
     var mask: UInt64 = 0xFF
-    for var i = 0; i < 8; ++i {
+    for i in 0..<8 {
       if (value & mask) == mask {
         return i
       }

stdlib/public/core/HashedCollections.swift.gyb

@@ -730,12 +730,14 @@ public func == <Element : Hashable>(lhs: Set<Element>, rhs: Set<Element>) -> Boo
     }
 
     let endIndex = lhsNative.endIndex
-    for var i = lhsNative.startIndex; i != endIndex; i = i.successor() {
-      let key = lhsNative.assertingGet(i)
+    var index = lhsNative.startIndex
+    while index != endIndex {
+      let key = lhsNative.assertingGet(index)
       let bridgedKey: AnyObject = _bridgeToObjectiveCUnconditional(key)
       let optRhsValue: AnyObject? = rhsCocoa.maybeGet(bridgedKey)
       if let rhsValue = optRhsValue {
         if key == _forceBridgeFromObjectiveC(rhsValue, Element.self) {
+          index = index.successor()
           continue
         }
       }
@@ -1247,13 +1249,14 @@ public func == <Key : Equatable, Value : Equatable>(
     }
 
     let endIndex = lhsNative.endIndex
-    for var index = lhsNative.startIndex; index != endIndex;
-        index._successorInPlace() {
+    var index = lhsNative.startIndex
+    while index != endIndex {
       let (key, value) = lhsNative.assertingGet(index)
       let optRhsValue: AnyObject? =
         rhsCocoa.maybeGet(_bridgeToObjectiveCUnconditional(key))
       if let rhsValue = optRhsValue {
         if value == _forceBridgeFromObjectiveC(rhsValue, Value.self) {
+          index._successorInPlace()
           continue
         }
       }
@@ -2130,7 +2133,7 @@ struct _Native${Self}Storage<${TypeParametersDecl}> :
   var description: String {
     var result = ""
 #if INTERNAL_CHECKS_ENABLED
-    for var i = 0; i != capacity; ++i {
+    for i in 0..<capacity {
       if isInitializedEntry(i) {
         let key = keyAt(i)
         result += "bucket \(i), ideal bucket = \(_bucket(key)), key = \(key)\n"
@@ -2618,7 +2621,7 @@ final internal class _Native${Self}StorageOwner<${TypeParametersDecl}>
     let bridged = _createBridgedNativeStorage(nativeStorage.capacity)
 
     // Bridge everything.
-    for var i = 0; i < nativeStorage.capacity; ++i {
+    for i in 0..<nativeStorage.capacity {
       if nativeStorage.isInitializedEntry(i) {
         let key = _bridgeToObjectiveCUnconditional(nativeStorage.keyAt(i))
 %if Self == 'Set':
@@ -3265,20 +3268,19 @@ internal enum _Variant${Self}Storage<${TypeParametersDecl}> : _HashStorageType {
 
     // Find the last bucket in the contiguous chain
     var lastInChain = hole
-    for var b = nativeStorage._next(lastInChain);
-      nativeStorage.isInitializedEntry(b);
-      b = nativeStorage._next(b) {
-      lastInChain = b
+    var bucket = nativeStorage._next(lastInChain)
+    while nativeStorage.isInitializedEntry(bucket) {
+      lastInChain = bucket
+      bucket = nativeStorage._next(bucket)
     }
-
     // Relocate out-of-place elements in the chain, repeating until
     // none are found.
     while hole != lastInChain {
       // Walk backwards from the end of the chain looking for
       // something out-of-place.
-      var b: Int
-      for b = lastInChain; b != hole; b = nativeStorage._prev(b) {
-        let idealBucket = nativeStorage._bucket(nativeStorage.keyAt(b))
+      var bucket: Int = lastInChain
+      while bucket != hole {
+        let idealBucket = nativeStorage._bucket(nativeStorage.keyAt(bucket))
 
         // Does this element belong between start and hole?  We need
         // two separate tests depending on whether [start,hole] wraps
@@ -3288,15 +3290,16 @@ internal enum _Variant${Self}Storage<${TypeParametersDecl}> : _HashStorageType {
         if start <= hole ? (c0 && c1) : (c0 || c1) {
           break // Found it
         }
+        bucket = nativeStorage._prev(bucket)
       }
 
-      if b == hole { // No out-of-place elements found; we're done adjusting
+      if bucket == hole { // No out-of-place elements found; we're done adjusting
         break
       }
 
       // Move the found element into the hole
-      nativeStorage.moveInitializeFrom(nativeStorage, at: b, toEntryAt: hole)
-      hole = b
+      nativeStorage.moveInitializeFrom(nativeStorage, at: bucket, toEntryAt: hole)
+      hole = bucket
     }
   }
 

stdlib/public/core/Prespecialized.swift

@@ -29,8 +29,8 @@ struct _Prespecialize {
         a[0] = a[j]
       }
 
-      for var i1 = 0; i1 < a.count; ++i1 {
-        for var i2 = 0; i2 < a.count; ++i2 {
+      for i1 in 0..<a.count {
+        for i2 in 0..<a.count {
           a[i1] = a[i2]
         }
       }

stdlib/public/core/StringCharacterView.swift

@@ -145,7 +145,7 @@ extension String.CharacterView : CollectionType {
           unicodeScalars[start].value)
       start._successorInPlace()
 
-      for ; start != end; start._successorInPlace() {
+      while start != end {
         // FIXME(performance): consider removing this "fast path".  A branch
         // that is hard to predict could be worse for performance than a few
         // loads from cache to fetch the property 'gcb1'.
@@ -158,6 +158,7 @@ extension String.CharacterView : CollectionType {
           break
         }
         gcb0 = gcb1
+        start._successorInPlace()
       }
 
       return start._position - startIndexUTF16

stdlib/public/core/Unicode.swift

@@ -705,9 +705,8 @@ public func transcode<
 
   var inputDecoder = inputEncoding.init()
   var hadError = false
-  for var scalar = inputDecoder.decode(&input);
-          !scalar.isEmptyInput();
-          scalar = inputDecoder.decode(&input) {
+  var scalar = inputDecoder.decode(&input);
+  while !scalar.isEmptyInput() {
     switch scalar {
     case .Result(let us):
       OutputEncoding.encode(us, output: output)
@@ -721,6 +720,7 @@ public func transcode<
         hadError = true
       }
     }
+    scalar = inputDecoder.decode(&input)
   }
   return hadError
 }

stdlib/public/core/UnsafePointer.swift.gyb

@@ -210,7 +210,9 @@ ${comment}
     _debugPrecondition(
       source < self || source >= self + count,
       "${Self}.assignBackwardFrom non-preceding overlapping range; use assignFrom instead")
-    for var i = count; --i >= 0; {
+    var i = count
+    while i >= 0 {
+      i -= 1
       self[i] = source[i]
     }
   }