stdlib: move the bulk of SequenceType algorithms to protocol extensions

rdar://19895265 Swift SVN r27269
2025-12-21 12:14:44 +01:00 · 2015-04-14 01:53:19 +00:00
parent 272371a3f5
commit d267b86cb6
24 changed files with 3235 additions and 809 deletions
--- a/stdlib/private/StdlibUnittest/StdlibUnittest.swift.gyb
+++ b/stdlib/private/StdlibUnittest/StdlibUnittest.swift.gyb
@@ -25,9 +25,9 @@ import ObjectiveC
 #endif

 public struct SourceLoc {
-  let file: String
-  let line: UWord
-  let comment: String?
+  public let file: String
+  public let line: UWord
+  public let comment: String?

  public init(_ file: String, _ line: UWord, comment: String? = nil) {
    self.file = file
@@ -135,13 +135,15 @@ public func expectEqual<T>(
 public func expectNotEqual<T : Equatable>(
    expected: T, actual: T,
    stackTrace: SourceLocStack? = nil,
-    file: String = __FILE__, line: UWord = __LINE__
+    file: String = __FILE__, line: UWord = __LINE__,
+    collectMoreInfo: (()->String)? = nil
 ) {
  if expected == actual {
    _anyExpectFailed = true
    println("check failed at \(file), line \(line)")
    _printStackTrace(stackTrace)
    println("unexpected value: \"\(actual)\" (of type \(_stdlib_getDemangledTypeName(actual)))")
+    if collectMoreInfo != nil { println(collectMoreInfo!()) }
    println()
  }
 }
@@ -150,11 +152,13 @@ public func expectNotEqual<T : Equatable>(
 // <rdar://problem/17015923> Array->NSArray implicit conversion insanity
 public func expectOptionalEqual<T : Equatable>(
    expected: T, actual: T?,
+    stackTrace: SourceLocStack? = nil,
    file: String = __FILE__, line: UWord = __LINE__
 ) {
  if (actual == nil) || expected != actual! {
    _anyExpectFailed = true
    println("check failed at \(file), line \(line)")
+    _printStackTrace(stackTrace)
    println("expected: \"\(expected)\" (of type \(_stdlib_getDemangledTypeName(expected)))")
    println("actual: \"\(actual)\" (of type \(_stdlib_getDemangledTypeName(actual)))")
    println()
@@ -163,12 +167,14 @@ public func expectOptionalEqual<T : Equatable>(

 public func expectEqual<T : Equatable>(
    expected: T?, actual: T?,
+    stackTrace: SourceLocStack? = nil,
    file: String = __FILE__, line: UWord = __LINE__
 ) {
  if (actual == nil) != (expected == nil)
    || actual != nil && expected! != actual! {
    _anyExpectFailed = true
    println("check failed at \(file), line \(line)")
+    _printStackTrace(stackTrace)
    println("expected: \"\(expected)\" (of type \(_stdlib_getDemangledTypeName(expected)))")
    println("actual: \"\(actual)\" (of type \(_stdlib_getDemangledTypeName(actual)))")
    println()
@@ -182,8 +188,7 @@ public func expectEqual<T : Equatable>(
 %    ('<T : Equatable>', '_UnitTestArray<T>'),
 %    ('<T : Equatable>', 'ArraySlice<T>'),
 %    ('<T : Equatable>', 'Array<T>'),
-%    ('<T, U : Equatable>', 'Dictionary<T, U>'),
-%    ('<T : ForwardIndexType>', 'T')]:
+%    ('<T, U : Equatable>', 'Dictionary<T, U>')]:

 public func expectEqual${Generic}(
    expected: ${EquatableType}, actual: ${EquatableType},
@@ -219,12 +224,14 @@ public func expectEqualSequence${Generic}(

 func _expectNotEqual${Generic}(
    expected: ${EquatableType}, actual: ${EquatableType},
-    file: String = __FILE__, line: UWord = __LINE__
+    file: String = __FILE__, line: UWord = __LINE__,
+    collectMoreInfo: (()->String)? = nil
 ) {
  if expected == actual {
    _anyExpectFailed = true
    println("check failed at \(file), line \(line)")
    println("unexpected value: \"\(actual)\" (of type \(_stdlib_getDemangledTypeName(actual)))")
+    if collectMoreInfo != nil { println(collectMoreInfo!()) }
    println()
  }
 }
@@ -248,26 +255,34 @@ public func expectOptionalEqual${Generic}(

 public func expectLE(
  expected: ${ComparableType}, actual: ${ComparableType},
-    file: String = __FILE__, line: UWord = __LINE__
+  stackTrace: SourceLocStack? = nil,
+  file: String = __FILE__, line: UWord = __LINE__,
+  collectMoreInfo: (()->String)? = nil
 ) {
  if !(expected <= actual) {
    _anyExpectFailed = true
    println("check failed at \(file), line \(line)")
+    _printStackTrace(stackTrace)
    println("expected: \"\(expected)\"")
    println("actual: \"\(actual)\"")
+    if collectMoreInfo != nil { println(collectMoreInfo!()) }
    println()
  }
 }

 public func expectGE(
  expected: ${ComparableType}, actual: ${ComparableType},
-    file: String = __FILE__, line: UWord = __LINE__
+  stackTrace: SourceLocStack? = nil,
+  file: String = __FILE__, line: UWord = __LINE__,
+  collectMoreInfo: (()->String)? = nil
 ) {
  if !(expected >= actual) {
    _anyExpectFailed = true
    println("check failed at \(file), line \(line)")
+    _printStackTrace(stackTrace)
    println("expected: \"\(expected)\"")
    println("actual: \"\(actual)\"")
+    if collectMoreInfo != nil { println(collectMoreInfo!()) }
    println()
  }
 }
@@ -361,7 +376,8 @@ public func expectFalse(
 public func expectEmpty<T>(
    value: Optional<T>,
    stackTrace: SourceLocStack? = nil,
-    file: String = __FILE__, line: UWord = __LINE__
+    file: String = __FILE__, line: UWord = __LINE__,
+    collectMoreInfo: (()->String)? = nil
 ) {
  if value != nil {
    _anyExpectFailed = true
@@ -369,6 +385,7 @@ public func expectEmpty<T>(
    _printStackTrace(stackTrace)
    println("expected optional to be empty")
    println("actual: \"\(value)\"")
+    if collectMoreInfo != nil { println(collectMoreInfo!()) }
    println()
  }
 }
@@ -1341,6 +1358,19 @@ public func checkComparable<T : Comparable>(
    collectMoreInfo: collectMoreInfo)
 }

+public struct CollectionMisuseResiliencyChecks {
+  public var callNextOnExhaustedGenerator: Bool = true
+
+  public static var all: CollectionMisuseResiliencyChecks {
+    return CollectionMisuseResiliencyChecks()
+  }
+
+  public static var none: CollectionMisuseResiliencyChecks {
+    return CollectionMisuseResiliencyChecks(
+      callNextOnExhaustedGenerator: false)
+  }
+}
+
 // Generate two overloads: one for _UnitTestArray (which will get
 // picked up when the caller passes a literal), and another that
 // accepts any appropriate Collection type.
@@ -1351,10 +1381,14 @@ public func checkComparable<T : Comparable>(

 public func checkGenerator<
  G : GeneratorType, ${genericParam}
-  where ${Element} == G.Element, ${Element} : Equatable
+  where ${Element} == G.Element
 >(
  expected: ${Expected},
-    generator: G, stackTrace: SourceLocStack
+  generator: G,
+  sameValue: (${Element}, ${Element}) -> Bool,
+  resiliencyChecks: CollectionMisuseResiliencyChecks = .all,
+  stackTrace: SourceLocStack,
+  collectMoreInfo: (()->String)? = nil
 ) {
  // Copying a `GeneratorType` is allowed.
  var mutableGen = generator
@@ -1362,73 +1396,322 @@ public func checkGenerator<
  while let e? = mutableGen.next() {
    actual.append(e)
  }
-  expectEqualSequence(expected, actual, stackTrace: stackTrace.withCurrentLoc())
+  expectEqualSequence(
+    expected, actual, sameValue,
+    stackTrace: stackTrace.withCurrentLoc(),
+    collectMoreInfo: collectMoreInfo)

+  if resiliencyChecks.callNextOnExhaustedGenerator {
    // Having returned `.None` once, a `GeneratorType` should not generate more
    // elements.
    for i in 0..<10 {
-    expectEmpty(mutableGen.next(), stackTrace: stackTrace.withCurrentLoc())
+      expectEmpty(
+        mutableGen.next(),
+        stackTrace: stackTrace.withCurrentLoc(),
+        collectMoreInfo: collectMoreInfo)
    }
  }
+}
+
+public func checkGenerator<
+  G : GeneratorType, ${genericParam}
+  where ${Element} == G.Element, ${Element} : Equatable
+>(
+  expected: ${Expected},
+  generator: G,
+  resiliencyChecks: CollectionMisuseResiliencyChecks = .all,
+  stackTrace: SourceLocStack,
+  collectMoreInfo: (()->String)? = nil
+) {
+  checkGenerator(
+    expected, generator, { $0 == $1 },
+    resiliencyChecks: resiliencyChecks,
+    stackTrace.withCurrentLoc(),
+    collectMoreInfo: collectMoreInfo)
+}
+
+public func checkSequence<
+  ${genericParam}, S : SequenceType
+  where S.Generator.Element == ${Element}
+>(
+  expected: ${Expected},
+  sequence: S,
+  sameValue: (${Element}, ${Element}) -> Bool,
+  resiliencyChecks: CollectionMisuseResiliencyChecks = .all,
+  stackTrace: SourceLocStack,
+  collectMoreInfo: (()->String)? = nil
+) {
+  let expectedCount: Int = numericCast(count(expected))
+  checkGenerator(
+    expected, sequence.generate(), sameValue,
+    resiliencyChecks: resiliencyChecks,
+    stackTrace.withCurrentLoc())
+  expectGE(
+    expectedCount, underestimateCount(sequence),
+    stackTrace: stackTrace.withCurrentLoc(),
+    collectMoreInfo: collectMoreInfo)
+}
+
+public func checkSequence<
+  ${genericParam}, S : SequenceType
+  where S.Generator.Element == ${Element}
+>(
+  expected: ${Expected},
+  sequence: S,
+  sameValue: (${Element}, ${Element}) -> Bool,
+  resiliencyChecks: CollectionMisuseResiliencyChecks = .all,
+  file: String = __FILE__, line: UWord = __LINE__,
+  collectMoreInfo: (()->String)? = nil
+) {
+  checkSequence(
+    expected, sequence, sameValue,
+    resiliencyChecks: resiliencyChecks,
+    SourceLocStack().with(SourceLoc(file, line)),
+    collectMoreInfo: collectMoreInfo)
+}

 public func checkSequence<
  ${genericParam}, S : SequenceType
  where S.Generator.Element == ${Element}, ${Element} : Equatable
 >(
  expected: ${Expected},
-  sequence: S, stackTrace: SourceLocStack
+  sequence: S,
+  resiliencyChecks: CollectionMisuseResiliencyChecks = .all,
+  stackTrace: SourceLocStack,
+  collectMoreInfo: (()->String)? = nil
 ) {
-  let expectedCount: Int = numericCast(count(expected))
-  checkGenerator(expected, sequence.generate(), stackTrace.withCurrentLoc())
-  expectGE(expectedCount, underestimateCount(sequence))
+  checkSequence(
+    expected, sequence, { $0 == $1 },
+    resiliencyChecks: resiliencyChecks,
+    stackTrace.withCurrentLoc(),
+    collectMoreInfo: collectMoreInfo)
 }

-public func checkCollection<
-    ${genericParam}, C : CollectionType
-  where C.Generator.Element == ${Element}, ${Element} : Equatable
+public func checkSequence<
+  ${genericParam}, S : SequenceType
+  where S.Generator.Element == ${Element}, ${Element} : Equatable
 >(
  expected: ${Expected},
-      collection: C, stackTrace: SourceLocStack
+  sequence: S,
+  resiliencyChecks: CollectionMisuseResiliencyChecks = .all,
+  file: String = __FILE__, line: UWord = __LINE__,
+  collectMoreInfo: (()->String)? = nil
+) {
+  checkSequence(
+    expected, sequence, { $0 == $1 },
+    resiliencyChecks: resiliencyChecks,
+    SourceLocStack().with(SourceLoc(file, line)),
+    collectMoreInfo: collectMoreInfo)
+}
+
+%for traversal in [ 'Forward', 'Bidirectional', 'RandomAccess' ]:
+
+public func check${traversal}Collection<
+  ${genericParam}, C : CollectionType
+  where
+  C.Generator.Element == ${Element},
+  C.Index : ${traversal}IndexType
+>(
+  expected: ${Expected},
+  collection: C,
+  sameValue: (${Element}, ${Element}) -> Bool,
+  resiliencyChecks: CollectionMisuseResiliencyChecks = .all,
+  stackTrace: SourceLocStack,
+  collectMoreInfo: (()->String)? = nil
 ) {
  // A `CollectionType` is a multi-pass `SequenceType`.
  for i in 0..<3 {
-    checkSequence(expected, collection, stackTrace.withCurrentLoc())
+    checkSequence(
+      expected, collection, sameValue,
+      resiliencyChecks: resiliencyChecks,
+      stackTrace.withCurrentLoc(),
+      collectMoreInfo: collectMoreInfo)
  }

-  expectEqual(count(expected).toIntMax(), count(collection).toIntMax(),
-      stackTrace: stackTrace.withCurrentLoc())
+  let expectedArray = Array(expected)
+
+  expectEqual(
+    count(expectedArray).toIntMax(),
+    count(collection).toIntMax(),
+    stackTrace: stackTrace.withCurrentLoc(),
+    collectMoreInfo: collectMoreInfo)

  for i in 0..<3 {
+    if true {
      let startIndex = collection.startIndex
      let endIndex = collection.endIndex

-    var actual: _UnitTestArray<${Element}> = []
-    var index = collection.startIndex
-    while index != collection.endIndex {
-      // Iteration should not change `startIndex` or `endIndex`.
-      expectEqual(startIndex, collection.startIndex)
-      expectEqual(endIndex, collection.endIndex)
+      for i in indices(collection) {
+        expectEqual(startIndex, collection.startIndex,
+          stackTrace: stackTrace.withCurrentLoc()) {
+          "Iteration should not change startIndex"
+        }
+        expectEqual(endIndex, collection.endIndex,
+          stackTrace: stackTrace.withCurrentLoc()) {
+          "Iteration should not change endIndex"
+        }
+      }
+    }

-      actual.append(collection[index])
+    var allIndices: [C.Index] = []
+    for i in indices(collection) {
+      allIndices.append(i)
+    }
+
+    if count(expectedArray) >= 2 {
+      for i in 0..<allIndices.count-1 {
+        var successor1 = allIndices[i].successor()
+        var successor2 = allIndices[i]
+        successor2++
+        var successor3 = allIndices[i]
+        ++successor3
+        for s in [ successor1, successor2, successor3 ] {
+          expectEqual(
+            allIndices[i + 1], s,
+            stackTrace: stackTrace.withCurrentLoc())
+          expectEqual(
+            expectedArray[i + 1],
+            collection[s],
+            sameValue,
+            stackTrace: stackTrace.withCurrentLoc())
+        }
+      }
+%   if traversal == "Bidirectional":
+      for i in 1..<allIndices.count {
+        var predecessor1 = allIndices[i].predecessor()
+        var predecessor2 = allIndices[i]
+        predecessor2--
+        var predecessor3 = allIndices[i]
+        --predecessor3
+        for p in [ predecessor1, predecessor2, predecessor3 ] {
+          expectEqual(
+            allIndices[i - 1], p,
+            stackTrace: stackTrace.withCurrentLoc())
+          expectEqual(
+            expectedArray[i - 1], collection[p],
+            sameValue,
+            stackTrace: stackTrace.withCurrentLoc())
+        }
+      }
+      for i in 1..<allIndices.count {
+        var index = allIndices[i]
+        --index
        ++index
+        expectEqual(
+          allIndices[i], index,
+          stackTrace: stackTrace.withCurrentLoc())
+        expectEqual(
+          expectedArray[i], collection[index],
+          sameValue,
+          stackTrace: stackTrace.withCurrentLoc())
+      }
+%   end
+    }
+
+    if true {
+      var allIndices2: [C.Index] = []
+      for i in indices(collection) {
+        allIndices2.append(i)
      }

      expectEqualSequence(
-      expected, actual, stackTrace: stackTrace.withCurrentLoc())
+        allIndices, allIndices2,
+        stackTrace: stackTrace.withCurrentLoc()) {
+        "iteration should not invalidate indices"
+      }
+
+      expectEqualSequence(
+        expectedArray,
+        allIndices._prext_map { collection[$0] },
+        sameValue,
+        stackTrace: stackTrace.withCurrentLoc())
+      expectEqualSequence(
+        expectedArray,
+        allIndices2._prext_map { collection[$0] },
+        sameValue,
+        stackTrace: stackTrace.withCurrentLoc())
    }
  }

-public func checkSliceableWithBidirectionalIndex<
-    ${genericParam}, S : Sliceable
-      where S.Generator.Element == ${Element},
-        S.SubSlice.Generator.Element == ${Element},
-        S.Index : BidirectionalIndexType,
+  // FIXME: more checks for bidirectional and random access collections.
+}
+
+public func check${traversal}Collection<
+  ${genericParam}, C : CollectionType
+  where
+  C.Generator.Element == ${Element},
+  C.Index : ${traversal}IndexType
+>(
+  expected: ${Expected},
+  collection: C,
+  sameValue: (${Element}, ${Element}) -> Bool,
+  resiliencyChecks: CollectionMisuseResiliencyChecks = .all,
+  file: String = __FILE__, line: UWord = __LINE__,
+  collectMoreInfo: (()->String)? = nil
+) {
+  check${traversal}Collection(
+    expected, collection, sameValue,
+    resiliencyChecks: resiliencyChecks,
+    SourceLocStack().with(SourceLoc(file, line)),
+    collectMoreInfo: collectMoreInfo)
+}
+
+public func check${traversal}Collection<
+  ${genericParam}, C : CollectionType
+  where
+  C.Generator.Element == ${Element},
+  C.Index : ${traversal}IndexType,
  ${Element} : Equatable
 >(
  expected: ${Expected},
-    sliceable: S, stackTrace: SourceLocStack) {
+  collection: C,
+  resiliencyChecks: CollectionMisuseResiliencyChecks = .all,
+  stackTrace: SourceLocStack,
+  collectMoreInfo: (()->String)? = nil
+) {
+  check${traversal}Collection(
+    expected, collection, { $0 == $1 },
+    resiliencyChecks: resiliencyChecks,
+    stackTrace.withCurrentLoc(),
+    collectMoreInfo: collectMoreInfo)
+}
+
+public func check${traversal}Collection<
+  ${genericParam}, C : CollectionType
+  where
+  C.Generator.Element == ${Element},
+  C.Index : ${traversal}IndexType,
+  ${Element} : Equatable
+>(
+  expected: ${Expected},
+  collection: C,
+  resiliencyChecks: CollectionMisuseResiliencyChecks = .all,
+  file: String = __FILE__, line: UWord = __LINE__,
+  collectMoreInfo: (()->String)? = nil
+) {
+  check${traversal}Collection(
+    expected, collection, { $0 == $1 },
+    resiliencyChecks: resiliencyChecks,
+    SourceLocStack().with(SourceLoc(file, line)),
+    collectMoreInfo: collectMoreInfo)
+}
+
+% end
+
+public func checkSliceableWithBidirectionalIndex<
+  ${genericParam}, S : Sliceable
+  where
+  S.Generator.Element == ${Element},
+  S.SubSlice.Generator.Element == ${Element},
+  S.Index : BidirectionalIndexType,
+  S.SubSlice.Index : BidirectionalIndexType,
+  ${Element} : Equatable
+>(
+  expected: ${Expected}, 
+  sliceable: S, stackTrace: SourceLocStack
+) {
  // A `Sliceable` is a `CollectionType`.
-  checkCollection(expected, sliceable, stackTrace.withCurrentLoc())
+  checkBidirectionalCollection(expected, sliceable, stackTrace.withCurrentLoc())

  let expectedArray = _UnitTestArray(expected)
  
@@ -1450,7 +1733,8 @@ public func checkSliceableWithBidirectionalIndex<
      }
      let expectedSlice = expectedArray[startNumericIndex..<endNumericIndex]
      let slice = sliceable[start..<end]
-      checkCollection(expectedSlice, slice, stackTrace.withCurrentLoc())
+      checkBidirectionalCollection(
+        expectedSlice, slice, stackTrace.withCurrentLoc())

      if end != sliceable.endIndex {
        ++end
@@ -1549,6 +1833,25 @@ public func expectEqualSequence<
    file: file, line: line, collectMoreInfo: collectMoreInfo)
 }

+public func expectEqualSequence<
+  Expected : SequenceType,
+  Actual : SequenceType,
+  T : Equatable,
+  U : Equatable
+  where Expected.Generator.Element == Actual.Generator.Element,
+     Expected.Generator.Element == (T, U)
+>(
+    expected: Expected, actual: Actual,
+    stackTrace: SourceLocStack? = nil,
+    file: String = __FILE__, line: UWord = __LINE__,
+    collectMoreInfo: (()->String)? = nil
+) {
+  expectEqualSequence(
+    expected, actual, { $0.0 == $1.0 && $0.1 == $1.1 },
+    stackTrace: stackTrace, file: file, line: line,
+    collectMoreInfo: collectMoreInfo)
+}
+
 public func expectEqualSequence<
  Expected: SequenceType,
  Actual: SequenceType
@@ -1901,26 +2204,26 @@ public func ~> <T> (

 public struct MinimalForwardIndex : ForwardIndexType {
  public init(position: Int, endIndex: Int) {
-    self._position = position
-    self._endIndex = endIndex
+    self.position = position
+    self.endIndex = endIndex
  }

  public init(position: Int, startIndex _: Int, endIndex: Int) {
-    self._position = position
-    self._endIndex = endIndex
+    self.position = position
+    self.endIndex = endIndex
  }

  public func successor() -> MinimalForwardIndex {
-    expectNotEqual(_endIndex, _position)
-    return MinimalForwardIndex(position: _position + 1, endIndex: _endIndex)
+    expectNotEqual(endIndex, position)
+    return MinimalForwardIndex(position: position + 1, endIndex: endIndex)
  }

-  internal var _position: Int
-  internal var _endIndex: Int
+  public let position: Int
+  public let endIndex: Int
 }

 public func == (lhs: MinimalForwardIndex, rhs: MinimalForwardIndex) -> Bool {
-  return lhs._position == rhs._position
+  return lhs.position == rhs.position
 }

 //===----------------------------------------------------------------------===//
@@ -1929,33 +2232,33 @@ public func == (lhs: MinimalForwardIndex, rhs: MinimalForwardIndex) -> Bool {

 public struct MinimalBidirectionalIndex : BidirectionalIndexType {
  public init(position: Int, startIndex: Int, endIndex: Int) {
-    self._position = position
-    self._startIndex = startIndex
-    self._endIndex = endIndex
+    self.position = position
+    self.startIndex = startIndex
+    self.endIndex = endIndex
  }

  public func successor() -> MinimalBidirectionalIndex {
-    expectNotEqual(_endIndex, _position)
+    expectNotEqual(endIndex, position)
    return MinimalBidirectionalIndex(
-      position: _position + 1, startIndex: _startIndex, endIndex: _endIndex)
+      position: position + 1, startIndex: startIndex, endIndex: endIndex)
  }

  public func predecessor() -> MinimalBidirectionalIndex {
-    expectNotEqual(_startIndex, _position)
+    expectNotEqual(startIndex, position)
    return MinimalBidirectionalIndex(
-      position: _position - 1, startIndex: _startIndex, endIndex: _endIndex)
+      position: position - 1, startIndex: startIndex, endIndex: endIndex)
  }

-  internal var _position: Int
-  internal var _startIndex: Int
-  internal var _endIndex: Int
+  public let position: Int
+  public let startIndex: Int
+  public let endIndex: Int
 }

 public func == (
  lhs: MinimalBidirectionalIndex,
  rhs: MinimalBidirectionalIndex
 ) -> Bool {
-  return lhs._position == rhs._position
+  return lhs.position == rhs.position
 }

 //===----------------------------------------------------------------------===//
@@ -1964,46 +2267,46 @@ public func == (

 public struct MinimalRandomAccessIndex : RandomAccessIndexType {
  public init(position: Int, startIndex: Int, endIndex: Int) {
-    self._position = position
-    self._startIndex = startIndex
-    self._endIndex = endIndex
+    self.position = position
+    self.startIndex = startIndex
+    self.endIndex = endIndex
  }

  public func successor() -> MinimalRandomAccessIndex {
-    expectNotEqual(_endIndex, _position)
+    expectNotEqual(endIndex, position)
    return MinimalRandomAccessIndex(
-      position: _position + 1, startIndex: _startIndex, endIndex: _endIndex)
+      position: position + 1, startIndex: startIndex, endIndex: endIndex)
  }

  public func predecessor() -> MinimalRandomAccessIndex {
-    expectNotEqual(_startIndex, _position)
+    expectNotEqual(startIndex, position)
    return MinimalRandomAccessIndex(
-      position: _position - 1, startIndex: _startIndex, endIndex: _endIndex)
+      position: position - 1, startIndex: startIndex, endIndex: endIndex)
  }

  public func distanceTo(other: MinimalRandomAccessIndex) -> Int {
-    return other._position - _position
+    return other.position - position
  }

  public func advancedBy(n: Int) -> MinimalRandomAccessIndex {
-    expectNotEqual(_endIndex, _position)
-    let newPosition = _position + n
-    expectLE(_startIndex, newPosition)
-    expectGE(_endIndex, newPosition)
+    expectNotEqual(endIndex, position)
+    let newPosition = position + n
+    expectLE(startIndex, newPosition)
+    expectGE(endIndex, newPosition)
    return MinimalRandomAccessIndex(
-      position: newPosition, startIndex: _startIndex, endIndex: _endIndex)
+      position: newPosition, startIndex: startIndex, endIndex: endIndex)
  }

-  internal var _position: Int
-  internal var _startIndex: Int
-  internal var _endIndex: Int
+  public let position: Int
+  public let startIndex: Int
+  public let endIndex: Int
 }

 public func == (
  lhs: MinimalRandomAccessIndex,
  rhs: MinimalRandomAccessIndex
 ) -> Bool {
-  return lhs._position == rhs._position
+  return lhs.position == rhs.position
 }

 //===----------------------------------------------------------------------===//
@@ -2014,20 +2317,20 @@ public func == (
 %  Self = 'Minimal%sCollection' % traversal
 %  Index = 'Minimal%sIndex' % traversal

-/// A minimal implementation of CollectionType with extra checks.
+/// A minimal implementation of `CollectionType` with extra checks.
 public struct ${Self}<T> : CollectionType {
  public init<S : SequenceType where S.Generator.Element == T>(
    _ s: S,
    underestimatedCount: UnderestimateCountBehavior = .Value(0)
  ) {
-    self._data = Array(s)
+    self._elements = Array(s)

    switch underestimatedCount {
    case .Precise:
-      self.underestimatedCount = _data.count
+      self.underestimatedCount = _elements.count

    case .Overestimate:
-      self.underestimatedCount = _data.count * 3 + 5
+      self.underestimatedCount = _elements.count * 3 + 5

    case .Value(let count):
      self.underestimatedCount = count
@@ -2035,25 +2338,151 @@ public struct ${Self}<T> : CollectionType {
  }

  public func generate() -> MinimalGenerator<T> {
-    return MinimalGenerator(_data)
+    return MinimalGenerator(_elements)
  }

  public var startIndex: ${Index} {
-    return ${Index}(position: 0, startIndex: 0, endIndex: _data.endIndex)
+    return ${Index}(
+      position: 0,
+      startIndex: 0,
+      endIndex: _elements.endIndex)
  }

  public var endIndex: ${Index} {
    return ${Index}(
-      position: _data.endIndex, startIndex: 0, endIndex: _data.endIndex)
+      position: _elements.endIndex,
+      startIndex: 0,
+      endIndex: _elements.endIndex)
  }

  public subscript(i: ${Index}) -> T {
-    return _data[i._position]
+    return _elements[i.position]
  }

  public var underestimatedCount: Int

-  internal let _data: [T]
+  internal let _elements: [T]
+}
+
+public func ~> <T> (
+  c: ${Self}<T>, _: (_UnderestimateCount, ())
+) -> Int {
+  return c.underestimatedCount
+}
+
+%end
+
+//===----------------------------------------------------------------------===//
+// Minimal***RangeReplaceableCollectionType
+//===----------------------------------------------------------------------===//
+
+%for traversal in [ 'Forward', 'Bidirectional', 'RandomAccess' ]:
+%  Self = 'Minimal%sRangeReplaceableCollectionType' % traversal
+%  Index = 'Minimal%sIndex' % traversal
+
+/// A minimal implementation of `RangeReplaceableCollectionType` with extra
+/// checks.
+public struct ${Self}<T> : RangeReplaceableCollectionType {
+
+  public init<S : SequenceType where S.Generator.Element == T>(
+    _ s: S,
+    underestimatedCount: UnderestimateCountBehavior = .Value(0)
+  ) {
+    self.elements = Array(s)
+
+    switch underestimatedCount {
+    case .Precise:
+      self.underestimatedCount = elements.count
+
+    case .Overestimate:
+      self.underestimatedCount = elements.count * 3 + 5
+
+    case .Value(let count):
+      self.underestimatedCount = count
+    }
+  }
+
+  public init() {
+    self.underestimatedCount = 0
+    self.elements = []
+  }
+
+  public func generate() -> MinimalGenerator<T> {
+    return MinimalGenerator(elements)
+  }
+
+  public var startIndex: ${Index} {
+    return ${Index}(
+      position: 0,
+      startIndex: 0,
+      endIndex: elements.endIndex)
+  }
+
+  public var endIndex: ${Index} {
+    return ${Index}(
+      position: elements.endIndex,
+      startIndex: 0,
+      endIndex: elements.endIndex)
+  }
+
+  public subscript(i: ${Index}) -> T {
+    return elements[i.position]
+  }
+
+  public mutating func reserveCapacity(n: Int) {
+    elements.reserveCapacity(n)
+    reservedCapacity = max(reservedCapacity, n)
+  }
+
+  public mutating func append(x: T) {
+    elements.append(x)
+  }
+
+  public mutating func extend<
+    S : SequenceType where S.Generator.Element == T
+  >(newElements: S) {
+    elements.extend(newElements)
+  }
+
+  public mutating func replaceRange<
+    C : CollectionType where C.Generator.Element == T
+  >(
+    subRange: Range<${Index}>, with newElements: C
+  ) {
+    elements.replaceRange(
+      subRange.startIndex.position..<subRange.endIndex.position,
+      with: newElements)
+  }
+
+  public mutating func insert(newElement: T, atIndex i: ${Index}) {
+    elements.insert(newElement, atIndex: i.position)
+  }
+
+  public mutating func splice<
+    S : CollectionType where S.Generator.Element == T
+  >(newElements: S, atIndex i: ${Index}) {
+    elements.splice(newElements, atIndex: i.position)
+  }
+
+  public mutating func removeAtIndex(i: ${Index}) -> T {
+    return elements.removeAtIndex(i.position)
+  }
+
+  public mutating func removeRange(subRange: Range<${Index}>) {
+    elements.removeRange(
+      subRange.startIndex.position..<subRange.endIndex.position
+    )
+  }
+
+  public mutating func removeAll(keepCapacity: Bool = false) {
+    // Ignore the value of `keepCapacity`.
+    elements.removeAll(keepCapacity: false)
+  }
+
+  public var underestimatedCount: Int
+  public var reservedCapacity: Int = 0
+
+  public var elements: [T]
 }

 public func ~> <T> (
--- a/stdlib/public/core/Algorithm.swift
+++ b/stdlib/public/core/Algorithm.swift
@@ -16,12 +16,8 @@ public func minElement<
     R : SequenceType
       where R.Generator.Element : Comparable>(elements: R)
  -> R.Generator.Element {
-  var g = elements.generate()
-  var result = g.next()!  
-  for e in GeneratorSequence(g) {
-    if e < result { result = e }
-  }
-  return result
+  // FIXME(prext): remove this function when protocol extensions land.
+  return elements._prext_minElement()!
 }

 /// Returns the maximum element in `elements`.  Requires:
@@ -30,12 +26,8 @@ public func maxElement<
     R : SequenceType
       where R.Generator.Element : Comparable>(elements: R)
  -> R.Generator.Element {
-  var g = elements.generate()
-  var result = g.next()!
-  for e in GeneratorSequence(g) {
-    if e > result { result = e }
-  }
-  return result
+  // FIXME(prext): remove this function when protocol extensions land.
+  return elements._prext_maxElement()!
 }

 /// Returns the first index where `value` appears in `domain` or `nil` if
@@ -45,12 +37,8 @@ public func maxElement<
 public func find<
  C: CollectionType where C.Generator.Element : Equatable
 >(domain: C, value: C.Generator.Element) -> C.Index? {
-  for i in indices(domain) {
-    if domain[i] == value {
-      return i
-    }
-  }
-  return nil
+  // FIXME(prext): remove this function when protocol extensions land.
+  return domain._prext_find(value)
 }

 /// Return the lesser of `x` and `y`
@@ -167,16 +155,8 @@ public func startsWith<
    S0.Generator.Element : Equatable
 >(s: S0, prefix: S1) -> Bool
 {
-  var prefixGenerator = prefix.generate()
-
-  for e0 in s {
-    var e1 = prefixGenerator.next()
-    if e1 == nil { return true }
-    if e0 != e1! {
-      return false
-    }
-  }
-  return prefixGenerator.next() != nil ? false : true
+  // FIXME(prext): remove this function when protocol extensions land.
+  return s._prext_startsWith(prefix)
 }

 /// Return true iff `s` begins with elements equivalent to those of
@@ -192,16 +172,8 @@ public func startsWith<
  @noescape isEquivalent: (S1.Generator.Element, S1.Generator.Element) -> Bool)
  -> Bool
 {
-  var prefixGenerator = prefix.generate()
-
-  for e0 in s {
-    var e1 = prefixGenerator.next()
-    if e1 == nil { return true }
-    if !isEquivalent(e0, e1!) {
-      return false
-    }
-  }
-  return prefixGenerator.next() != nil ? false : true
+  // FIXME(prext): remove this function when protocol extensions land.
+  return s._prext_startsWith(prefix, isEquivalent: isEquivalent)
 }

 /// The `GeneratorType` for `EnumerateSequence`.  `EnumerateGenerator`
@@ -290,7 +262,8 @@ public struct EnumerateSequence<Base : SequenceType> : SequenceType {
 public func enumerate<Seq : SequenceType>(
  base: Seq
 ) -> EnumerateSequence<Seq> {
-  return EnumerateSequence(base)
+  // FIXME(prext): remove this function when protocol extensions land.
+  return base._prext_enumerate()
 }

 /// Return `true` iff `a1` and `a2` contain the same elements in the
@@ -300,22 +273,9 @@ public func equal<
  where
    S1.Generator.Element == S2.Generator.Element,
    S1.Generator.Element : Equatable
->(a1: S1, a2: S2) -> Bool
-{
-  var g1 = a1.generate()
-  var g2 = a2.generate()
-  while true {
-    var e1 = g1.next()
-    var e2 = g2.next()
-    if (e1 != nil) && (e2 != nil) {
-      if e1! != e2! {
-        return false
-      }
-    }
-    else {
-      return (e1 == nil) == (e2 == nil)
-    }
-  }
+>(a1: S1, a2: S2) -> Bool {
+  // FIXME(prext): remove this function when protocol extensions land.
+  return a1._prext_equalElements(a2)
 }

 /// Return true iff `a1` and `a2` contain equivalent elements, using
@@ -328,22 +288,9 @@ public func equal<
    S1.Generator.Element == S2.Generator.Element
 >(a1: S1, a2: S2,
  @noescape isEquivalent: (S1.Generator.Element, S1.Generator.Element) -> Bool)
-  -> Bool
-{
-  var g1 = a1.generate()
-  var g2 = a2.generate()
-  while true {
-    var e1 = g1.next()
-    var e2 = g2.next()
-    if (e1 != nil) && (e2 != nil) {
-      if !isEquivalent(e1!, e2!) {
-        return false
-      }
-    }
-    else {
-      return (e1 == nil) == (e2 == nil)
-    }
-  }
+  -> Bool {
+  // FIXME(prext): remove this function when protocol extensions land.
+  return a1._prext_equalElements(a2, isEquivalent: isEquivalent)
 }

 /// Return true iff a1 precedes a2 in a lexicographical ("dictionary")
@@ -354,26 +301,8 @@ public func lexicographicalCompare<
    S1.Generator.Element == S2.Generator.Element,
    S1.Generator.Element : Comparable>(
  a1: S1, a2: S2) -> Bool {
-  var g1 = a1.generate()
-  var g2 = a2.generate()
-  while true {
-    var e1_ = g1.next()
-    var e2_ = g2.next()
-    if let e1? = e1_ {
-      if let e2? = e2_ {
-        if e1 < e2 {
-          return true
-        }
-        if e2 < e1 {
-          return false
-        }
-        continue // equivalent
-      }
-      return false
-    }
-
-    return e2_ != nil
-  }
+  // FIXME(prext): remove this function when protocol extensions land.
+  return a1._prext_lexicographicalCompare(a2)
 }

 /// Return true iff `a1` precedes `a2` in a lexicographical ("dictionary")
@@ -391,44 +320,24 @@ public func lexicographicalCompare<
  @noescape isOrderedBefore less: (S1.Generator.Element, S1.Generator.Element)
  -> Bool
 ) -> Bool {
-  var g1 = a1.generate()
-  var g2 = a2.generate()
-  while true {
-    var e1_ = g1.next()
-    var e2_ = g2.next()
-    if let e1? = e1_ {
-      if let e2? = e2_ {
-        if less(e1, e2) {
-          return true
-        }
-        if less(e2, e1) {
-          return false
-        }
-        continue // equivalent
-      }
-      return false
-    }
-    return e2_ != nil
-  }
+  // FIXME(prext): remove this function when protocol extensions land.
+  return a1._prext_lexicographicalCompare(a2, isOrderedBefore: less)
 }

 /// Return `true` iff an element in `seq` satisfies `predicate`.
 public func contains<
  S : SequenceType, L : BooleanType
 >(seq: S, @noescape predicate: (S.Generator.Element) -> L) -> Bool {
-  for a in seq {
-    if predicate(a) {
-      return true
-    }
-  }
-  return false
+  // FIXME(prext): remove this function when protocol extensions land.
+  return seq._prext_contains({ predicate($0).boolValue })
 }

 /// Return `true` iff `x` is in `seq`.
 public func contains<
  S : SequenceType where S.Generator.Element : Equatable
 >(seq: S, x: S.Generator.Element) -> Bool {
-  return contains(seq, { $0 == x })
+  // FIXME(prext): remove this function when protocol extensions land.
+  return seq._prext_contains(x)
 }

 /// Return the result of repeatedly calling `combine` with an
@@ -437,9 +346,6 @@ public func contains<
 public func reduce<S : SequenceType, U>(
  sequence: S, initial: U, @noescape combine: (U, S.Generator.Element) -> U
 ) -> U {
-  var result = initial
-  for element in sequence {
-    result = combine(result, element)
-  }
-  return result
+  // FIXME(prext): remove this function when protocol extensions land.
+  return sequence._prext_reduce(initial, combine: combine)
 }
--- a/stdlib/public/core/Arrays.swift.gyb
+++ b/stdlib/public/core/Arrays.swift.gyb
@@ -494,16 +494,23 @@ extension ${Self} : _ArrayType {

  /// `true` if and only if the `${Self}` is empty
  public var isEmpty: Bool {
-    return count == 0
+    // FIXME(prext): remove this function when protocol extensions land.
+    return self._prext_isEmpty
  }
  
  /// The first element, or `nil` if the array is empty
  public var first: Element? {
-    return Swift.first(self)
+    // FIXME(prext): remove this function when protocol extensions land.
+    return self._prext_first
  }
  
  /// The last element, or `nil` if the array is empty
  public var last: Element? {
+    // FIXME(prext): remove this function when protocol extensions land.
+
+    // FIXME: we can't use the commented-out code because the optimizer
+    // crashes.  <rdar://problem/20514925> Optimizer crashes [...]
+    // return self._prext_last
    return Swift.last(self)
  }
  
@@ -656,7 +663,8 @@ extension ${Self} : _ArrayType {
  /// `combine(combine(...combine(combine(initial, self[0]),
  /// self[1]),...self[count-2]), self[count-1])`.
  public func reduce<U>(initial: U, @noescape combine: (U, T) -> U) -> U {
-    return Swift.reduce(self, initial, combine)
+    // FIXME(prext): remove this function when protocol extensions land.
+    return self._prext_reduce(initial, combine: combine)
  }

  /// Sort `self` in-place according to `isOrderedBefore`.  Requires:
@@ -684,34 +692,28 @@ extension ${Self} : _ArrayType {
  /// Return ${a_Self} containing the results of calling
  /// `transform(x)` on each element `x` of `self`
  public func map<U>(transform: (T) -> U) -> ${Self}<U> {
-    // Should call Swift.map here, but there's a compiler bug:
-    // <rdar://problem/19763792> Calling Swift.map from Array.map causes
-    // Assertion failed: UnresolvedDot in wrong phase
-    return ${Self}<U>(lazy(self).map(transform))
+    // FIXME(prext): remove this function when protocol extensions land.
+    return ${Self}<U>(self._prext_map(transform))
  }

  /// Return ${a_Self} containing the results of calling
  /// `transform(x)` on each element `x` of `self` and flattening the result.
  public func flatMap<U>(@noescape transform: (T) -> ${Self}<U>) -> ${Self}<U> {
-    var result: ${Self}<U> = []
-    for element in self {
-      result.extend(transform(element))
-    }
-    return result
+    // FIXME(prext): remove this function when protocol extensions land.
+    return ${Self}<U>(self._prext_flatMap(transform))
  }

  /// A ${Self} containing the elements of `self` in reverse order
  public func reverse() -> ${Self} {
-    return ${Self}(lazy(self).reverse())
+    // FIXME(prext): remove this function when protocol extensions land.
+    return ${Self}(self._prext_reverse())
  }

  /// Return ${a_Self} containing the elements `x` of `self` for which
  /// `includeElement(x)` is `true`
  public func filter(includeElement: (T) -> Bool) -> ${Self} {
-    // Should call Swift.filter() here, but there's a compiler bug:
-    // <rdar://problem/19763792> Calling Swift.map from Array.map causes
-    // Assertion failed: UnresolvedDot in wrong phase
-    return ${Self}(lazy(self).filter(includeElement))
+    // FIXME(prext): remove this function when protocol extensions land.
+    return self._prext_filter(includeElement)
  }
 }

--- a/stdlib/public/core/CMakeLists.txt
+++ b/stdlib/public/core/CMakeLists.txt
@@ -69,6 +69,7 @@ set(SWIFTLIB_ESSENTIAL
  OutputStream.swift
  Pointer.swift
  Policy.swift
+  ProtocolExtensions.swift.gyb
  REPL.swift
  Range.swift
  RangeMirrors.swift.gyb
--- a/stdlib/public/core/Collection.swift
+++ b/stdlib/public/core/Collection.swift
@@ -66,6 +66,12 @@ public protocol _CollectionType : _SequenceType {
  subscript(_i: Index) -> _Element {get}
 }

+public protocol _CollectionDefaultsType : _CollectionType {
+}
+
+extension _CollectionDefaultsType {
+}
+
 /// A multi-pass *sequence* with addressable positions.
 ///
 /// Positions are represented by an associated `Index` type.  Whereas
@@ -80,7 +86,9 @@ public protocol _CollectionType : _SequenceType {
 ///   for i in startIndex..<endIndex {
 ///     let x = self[i]
 ///   }
-public protocol CollectionType : _CollectionType, SequenceType {
+public protocol CollectionType
+  : _CollectionType, _CollectionDefaultsType, SequenceType {
+
  /// Access the element indicated by `position`.
  ///
  /// Requires: `position` indicates a valid position in `self` and
@@ -124,12 +132,14 @@ public func ~> <T : _CollectionType, R>(

 /// Returns `true` iff `x` is empty.
 public func isEmpty<C: CollectionType>(x: C) -> Bool {
-  return x.startIndex == x.endIndex
+  // FIXME(prext): remove this function when protocol extensions land.
+  return x._prext_isEmpty
 }

 /// Returns the first element of `x`, or `nil` if `x` is empty.
 public func first<C: CollectionType>(x: C) -> C.Generator.Element? {
-  return isEmpty(x) ? nil : x[x.startIndex]
+  // FIXME(prext): remove this function when protocol extensions land.
+  return x._prext_first
 }

 /// Returns the last element of `x`, or `nil` if `x` is empty.
@@ -213,7 +223,8 @@ public struct IndexingGenerator<
 /// all valid subscript arguments for `x`, omitting its `endIndex`.
 public func indices<
    C : CollectionType>(x: C) -> Range<C.Index> {
-  return Range(start: x.startIndex, end: x.endIndex)
+  // FIXME(prext): remove this function when protocol extensions land.
+  return x._prext_indices
 }

 /// A *generator* that adapts a *collection* `C` and any *sequence* of
--- a/stdlib/public/core/CompilerProtocols.swift
+++ b/stdlib/public/core/CompilerProtocols.swift
@@ -66,7 +66,7 @@ public protocol _SequenceType {
 ///
 /// Its requirements are inherited by `SequenceType` and thus must
 /// be satisfied by types conforming to that protocol.
-public protocol _Sequence_Type : _SequenceType {
+public protocol _Sequence_Type : _SequenceType, _SequenceDefaultsType {
  /// A type whose instances can produce the elements of this
  /// sequence, in order.
  typealias Generator : GeneratorType
@@ -79,6 +79,25 @@ public protocol _Sequence_Type : _SequenceType {
  func generate() -> Generator
 }

+public protocol _SequenceDefaultsType {
+  /// A type that provides the *sequence*\ 's iteration interface and
+  /// encapsulates its iteration state.
+  typealias Generator : GeneratorType
+
+  /// Return a *generator* over the elements of this *sequence*.  The
+  /// *generator*\ 's next element is the first element of the
+  /// sequence.
+  ///
+  /// Complexity: O(1)
+  func generate() -> Generator
+}
+
+extension _SequenceDefaultsType {
+}
+
+extension _SequenceDefaultsType {
+}
+
 /// A type that can be iterated with a `for`\ ...\ `in` loop.
 ///
 /// `SequenceType` makes no requirement on conforming types regarding
--- a/stdlib/public/core/Filter.swift.gyb
+++ b/stdlib/public/core/Filter.swift.gyb
@@ -172,7 +172,8 @@ public struct FilterCollectionView<Base : CollectionType> : CollectionType {
 public func filter<S : SequenceType>(
  source: S, includeElement: (S.Generator.Element) -> Bool
 ) -> [S.Generator.Element] {
-  return lazy(source).filter(includeElement).array
+  // FIXME(prext): remove this function when protocol extensions land.
+  return source._prext_filter(includeElement)
 }

 % traversals = ('Forward', 'Bidirectional', 'RandomAccess')
@@ -200,6 +201,7 @@ extension ${Self} {
 public func filter<C : CollectionType>(
  source: C, includeElement: (C.Generator.Element)->Bool
 ) -> FilterCollectionView<C> {
+  // FIXME(prext): remove this function when protocol extensions land.
  return FilterCollectionView(_base: source, _include: includeElement)
 }
 */
--- a/stdlib/public/core/Map.swift.gyb
+++ b/stdlib/public/core/Map.swift.gyb
@@ -70,7 +70,8 @@ public func ~> <Base : SequenceType, T> (
 public func map<S : SequenceType, T>(
  source: S, transform: (S.Generator.Element) -> T
 ) -> [T] {
-  return lazy(source).map(transform).array
+  // FIXME(prext): remove this function when protocol extensions land.
+  return source._prext_map(transform)
 }

 /// Return an `Array` containing the results of mapping `transform`
@@ -78,11 +79,8 @@ public func map<S : SequenceType, T>(
 public func flatMap<S : SequenceType, T>(
  source: S, @noescape transform: (S.Generator.Element) -> [T]
 ) -> [T] {
-  var result: [T] = []
-  for element in source {
-    result.extend(transform(element))
-  }
-  return result
+  // FIXME(prext): remove this function when protocol extensions land.
+  return source._prext_flatMap(transform)
 }

 //===--- Collections ------------------------------------------------------===//
@@ -138,7 +136,8 @@ public func ~> <Base: CollectionType, T> (
 public func map<C : CollectionType, T>(
  source: C, transform: (C.Generator.Element) -> T
 ) -> [T] {
-  return lazy(source).map(transform).array
+  // FIXME(prext): remove this function when protocol extensions land.
+  return source._prext_map(transform)
 }

 /// Return an `Array` containing the results of mapping `transform`
@@ -146,11 +145,8 @@ public func map<C : CollectionType, T>(
 public func flatMap<C : CollectionType, T>(
  source: C, transform: (C.Generator.Element) -> [T]
 ) -> [T] {
-  var result: [T] = []
-  for elements in map(source, transform) {
-    result.extend(elements)
-  }
-  return result
+  // FIXME(prext): remove this function when protocol extensions land.
+  return source._prext_flatMap(transform)
 }

 //===--- Support for lazy(s) ----------------------------------------------===//
--- a/stdlib/public/core/ProtocolExtensions.swift.gyb
+++ b/stdlib/public/core/ProtocolExtensions.swift.gyb
@@ -0,0 +1,527 @@
+//===--- ProtocolExtensions.swift.gyb -------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+%{
+
+# We know we will eventually get a SequenceType.Element type.  Define
+# a shorthand that we can use today.
+GElement = "Generator.Element"
+
+}%
+
+//===----------------------------------------------------------------------===//
+// enumerate()
+//===----------------------------------------------------------------------===//
+
+extension SequenceType {
+  /// Return a lazy `SequenceType` containing pairs (*n*, *x*), where
+  /// *n*\ s are consecutive `Int`\ s starting at zero, and *x*\ s are
+  /// the elements of `base`::
+  ///
+  ///   > for (n, c) in enumerate("Swift") { println("\(n): '\(c)'" ) }
+  ///   0: 'S'
+  ///   1: 'w'
+  ///   2: 'i'
+  ///   3: 'f'
+  ///   4: 't'
+  final public func _prext_enumerate() -> EnumerateSequence<Self> {
+    return EnumerateSequence(self)
+  }
+}
+
+//===----------------------------------------------------------------------===//
+// minElement(), maxElement()
+//===----------------------------------------------------------------------===//
+
+% # Generate two versions: with explicit predicates and with
+% # a Comparable requirement.
+% for preds in [ True, False ]:
+
+extension SequenceType ${"" if preds else "where Self.Generator.Element : Comparable"} {
+
+  /// Returns the minimum element in `self`.
+  ///
+  /// Complexity: O(count(elements))
+%   if preds:
+  ///
+  /// Requires: `isOrderedBefore` is a `strict weak ordering
+  /// <http://en.wikipedia.org/wiki/Strict_weak_order#Strict_weak_orderings>`__
+  /// over `self`."""
+%   end
+  final public func _prext_minElement(
+%   if preds:
+    @noescape isOrderedBefore: (${GElement}, ${GElement}) -> Bool
+%   end
+  ) -> ${GElement}? {
+    var g = generate()
+    if var result? = g.next() {
+      for e in GeneratorSequence(g) {
+%   if preds:
+        if isOrderedBefore(e, result) { result = e }
+%   else:
+        if e < result { result = e }
+%   end
+      }
+      return result
+    }
+    return nil
+  }
+
+  /// Returns the maximum element in `self`.
+  ///
+  /// Complexity: O(count(elements))
+%   if preds:
+  ///
+  /// Requires: `isOrderedBefore` is a `strict weak ordering
+  /// <http://en.wikipedia.org/wiki/Strict_weak_order#Strict_weak_orderings>`__
+  /// over `self`."""
+%   end
+  final public func _prext_maxElement(
+%   if preds:
+    @noescape isOrderedBefore: (${GElement}, ${GElement}) -> Bool
+%   end
+  ) -> ${GElement}? {
+    var g = generate()
+    if var result? = g.next() {
+      for e in GeneratorSequence(g) {
+%   if preds:
+        if isOrderedBefore(result, e) { result = e }
+%   else:
+        if e > result { result = e }
+%   end
+      }
+      return result
+    }
+    return nil
+  }
+}
+
+% end
+
+//===----------------------------------------------------------------------===//
+// startsWith()
+//===----------------------------------------------------------------------===//
+
+% # Generate two versions: with explicit predicates and with
+% # an Equatable requirement.
+% for preds in [ True, False ]:
+
+extension SequenceType ${"" if preds else "where Self.Generator.Element : Equatable"} {
+
+%   if preds:
+  /// Return true iff `s` begins with elements equivalent to those of
+  /// `prefix`, using `isEquivalent` as the equivalence test.
+  ///
+  /// Requires: `isEquivalent` is an `equivalence relation
+  /// <http://en.wikipedia.org/wiki/Equivalence_relation>`_
+%   else:
+  /// Return true iff the the initial elements of `s` are equal to `prefix`.
+%   end
+  final public func _prext_startsWith<
+    S : SequenceType where S.${GElement} == ${GElement}
+  >(
+    prefix: S${"," if preds else ""}
+%   if preds:
+    @noescape isEquivalent: (${GElement}, ${GElement}) -> Bool
+%   end
+    ) -> Bool {
+    var prefixGenerator = prefix.generate()
+    for e0 in self {
+      if let e1? = prefixGenerator.next() {
+        if ${"!isEquivalent(e0, e1)" if preds else "e0 != e1"} {
+          return false
+        }
+      }
+      else {
+        return true
+      }
+    }
+    return prefixGenerator.next() != nil ? false : true
+  }
+}
+
+% end
+
+//===----------------------------------------------------------------------===//
+// equalElements()
+//===----------------------------------------------------------------------===//
+
+% # Generate two versions: with explicit predicates and with
+% # an Equatable requirement.
+% for preds in [ True, False ]:
+
+extension SequenceType ${"" if preds else "where Self.Generator.Element : Equatable"} {
+
+%   if preds:
+  /// Return true iff `a1` and `a2` contain equivalent elements, using
+  /// `isEquivalent` as the equivalence test.
+  ///
+  /// Requires: `isEquivalent` is an `equivalence relation
+  /// <http://en.wikipedia.org/wiki/Equivalence_relation>`_
+%   else:
+  /// Return `true` iff `self` and `s` contain the same elements in the
+  /// same order.
+%   end
+  final public func _prext_equalElements<
+    S : SequenceType where S.${GElement} == ${GElement}
+  >(
+    s: S${"," if preds else ""}
+%   if preds:
+    @noescape isEquivalent: (${GElement}, ${GElement}) -> Bool
+%   end
+  ) -> Bool {
+    var g1 = self.generate()
+    var g2 = s.generate()
+    while true {
+      switch (g1.next(), g2.next()) {
+      case let (e1?, e2?):
+%   if preds:
+        if !isEquivalent(e1, e2) {
+%   else:
+        if e1 != e2 {
+%   end
+          return false
+        }
+      case (_?, nil),
+           (nil, _?):
+        return false
+      case (nil, nil):
+        return true
+      }
+    }
+  }
+}
+
+% end
+
+//===----------------------------------------------------------------------===//
+// lexicographicalCompare()
+//===----------------------------------------------------------------------===//
+
+% # Generate two versions: with explicit predicates and with
+% # Comparable requirement.
+% for preds in [ True, False ]:
+
+%   if preds:
+/// Return true iff `a1` precedes `a2` in a lexicographical ("dictionary")
+/// ordering, using `isOrderedBefore` as the comparison between elements.
+///
+/// Requires: isOrderedBefore` is a `strict weak ordering
+/// <http://en.wikipedia.org/wiki/Strict_weak_order#Strict_weak_orderings>`__
+/// over the elements of `a1` and `a2`.
+%   else:
+/// Return true iff a1 precedes a2 in a lexicographical ("dictionary")
+/// ordering, using "<" as the comparison between elements.
+%   end
+extension SequenceType ${"" if preds else "where Self.Generator.Element : Comparable"} {
+  final public func _prext_lexicographicalCompare<
+    S : SequenceType where S.${GElement} == ${GElement}
+  >(
+    s: S${"," if preds else ""}
+%   if preds:
+    @noescape isOrderedBefore less: (${GElement}, ${GElement}) -> Bool
+%   end
+  ) -> Bool {
+    var g1 = self.generate()
+    var g2 = s.generate()
+    while true {
+      if let e1? = g1.next() {
+        if let e2? = g2.next() {
+          if ${"less(e1, e2)" if preds else "e1 < e2"} {
+            return true
+          }
+          if ${"less(e2, e1)" if preds else "e2 < e1"} {
+            return false
+          }
+          continue // equivalent
+        }
+        return false
+      }
+
+      return g2.next() != nil
+    }
+  }
+}
+
+% end
+
+//===----------------------------------------------------------------------===//
+// contains()
+//===----------------------------------------------------------------------===//
+
+extension SequenceType where Self.Generator.Element : Equatable {
+  /// Return `true` iff `x` is in `self`.
+  final public func _prext_contains(element: ${GElement}) -> Bool {
+    // FIXME: dynamic dispatch for Set and Dictionary.
+    for e in self {
+      if e == element {
+        return true
+      }
+    }
+    return false
+  }
+}
+
+extension SequenceType {
+  /// Return `true` iff an element in `self` satisfies `predicate`.
+  final public func _prext_contains(
+    @noescape predicate: (${GElement}) -> Bool
+  ) -> Bool {
+    for e in self {
+      if predicate(e) {
+        return true
+      }
+    }
+    return false
+  }
+}
+
+//===----------------------------------------------------------------------===//
+// reduce()
+//===----------------------------------------------------------------------===//
+
+extension SequenceType {
+  /// Return the result of repeatedly calling `combine` with an
+  /// accumulated value initialized to `initial` and each element of
+  /// `self`, in turn, i.e. return
+  /// `combine(combine(...combine(combine(initial, self[0]),
+  /// self[1]),...self[count-2]), self[count-1])`.
+  final public func _prext_reduce<T>(
+    initial: T, @noescape combine: (T, ${GElement}) -> T
+  ) -> T {
+    var result = initial
+    for element in self {
+      result = combine(result, element)
+    }
+    return result
+  }
+}
+
+//===----------------------------------------------------------------------===//
+// reverse()
+//===----------------------------------------------------------------------===//
+
+extension SequenceType {
+  /// Return an `Array` containing the elements of `self` in reverse
+  /// order.
+  final public func _prext_reverse() -> [${GElement}] {
+    // FIXME(performance): optimize to 1 pass?  But Array(self) can be
+    // optimized to a memcpy() sometimes.  Those cases are usually collections,
+    // though.
+    var result = Array(self)
+    let count = result.count
+    for i in 0..<count/2 {
+      swap(&result[i], &result[count - i - 1])
+    }
+    return result
+  }
+}
+
+extension CollectionType where Self.Index : BidirectionalIndexType {
+  /// Return a lazy `CollectionType` containing the elements of `self`
+  /// in reverse order.
+  final public func _prext_reverse() -> BidirectionalReverseView<Self> {
+    return BidirectionalReverseView(self)
+  }
+}
+
+extension CollectionType where Self.Index : RandomAccessIndexType {
+  /// Return a lazy `CollectionType` containing the elements of `self`
+  /// in reverse order.
+  final public func _prext_reverse() -> RandomAccessReverseView<Self> {
+    return RandomAccessReverseView(self)
+  }
+}
+
+//===----------------------------------------------------------------------===//
+// filter()
+//===----------------------------------------------------------------------===//
+
+// We would like to make filter() a protocol requirement, and dynamically
+// dispatched, but Swift generics don't allow us to express this.
+// rdar://20477576
+
+extension SequenceType {
+  /// Return an `Array` containing the elements of `self`,
+  /// in order, that satisfy the predicate `includeElement`.
+  final public func _prext_filter(
+    @noescape includeElement: (${GElement}) -> Bool
+  ) -> [${GElement}] {
+    var result: [${GElement}] = []
+    for e in self {
+      if includeElement(e) {
+        result.append(e)
+      }
+    }
+    return result
+  }
+}
+
+extension RangeReplaceableCollectionType {
+  /// Return an `Array` containing the elements of `self`,
+  /// in order, that satisfy the predicate `includeElement`.
+  final public func _prext_filter(
+    @noescape includeElement: (${GElement}) -> Bool
+  ) -> Self {
+    var result = Self()
+    for e in self {
+      if includeElement(e) {
+        result.append(e)
+      }
+    }
+    return result
+  }
+}
+
+//===----------------------------------------------------------------------===//
+// map()
+//===----------------------------------------------------------------------===//
+
+extension SequenceType {
+  /// Return an `Array` containing the results of mapping `transform`
+  /// over `self`.
+  final public func _prext_map<T>(
+    @noescape transform: (${GElement}) -> T
+  ) -> [T] {
+    var result: [T] = []
+    result.reserveCapacity(underestimateCount(self))
+    for element in self {
+      result.append(transform(element))
+    }
+    return result
+  }
+}
+
+//===----------------------------------------------------------------------===//
+// flatMap()
+//===----------------------------------------------------------------------===//
+
+extension SequenceType {
+  /// Return an `Array` containing the results of mapping `transform`
+  /// over `self` and flattening the result.
+  final public func _prext_flatMap<S : SequenceType>(
+    @noescape transform: (${GElement}) -> S
+  ) -> [S.${GElement}] {
+    var result: [S.${GElement}] = []
+    for element in self {
+      result.extend(transform(element))
+    }
+    return result
+  }
+}
+
+extension SequenceType {
+  /// Return an `Array` containing the non-nil results of mapping `transform`
+  /// over `self`.
+  final public func _prext_flatMap<T>(
+    @noescape transform: (${GElement}) -> T?
+  ) -> [T] {
+    var result: [T] = []
+    for element in self {
+      if let newElement? = transform(element) {
+        result.append(newElement)
+      }
+    }
+    return result
+  }
+}
+
+//===----------------------------------------------------------------------===//
+// zip()
+//===----------------------------------------------------------------------===//
+
+extension SequenceType {
+  /// Returns a sequence of pairs built out of two underlying sequences,
+  /// where the elements of the `i`\ th pair are the `i`\ th elements
+  /// of each underlying sequence.
+  final public func _prext_zip<S : SequenceType>(s: S) -> Zip2<Self, S> {
+    return Zip2(self, s)
+  }
+}
+
+// FIXME: we could have an overload on collections that returns a collection
+// and preserves the index kind.  Zip2 is only a sequence.
+
+//===----------------------------------------------------------------------===//
+// isEmpty
+//===----------------------------------------------------------------------===//
+
+extension CollectionType {
+  // FIXME: dynamic dispatch for Set and Dictionary.
+  final public var _prext_isEmpty: Bool {
+    return startIndex == endIndex
+  }
+}
+
+//===----------------------------------------------------------------------===//
+// first
+//===----------------------------------------------------------------------===//
+
+extension CollectionType {
+  final public var _prext_first: Generator.Element? {
+    return _prext_isEmpty ? nil : self[startIndex]
+  }
+}
+
+//===----------------------------------------------------------------------===//
+// find()
+//===----------------------------------------------------------------------===//
+
+extension CollectionType where Self.${GElement} : Equatable {
+  /// Returns the first index where `value` appears in `self` or `nil` if
+  /// `value` is not found.
+  ///
+  /// Complexity: O(\ `self.count()`\ )
+  final public func _prext_find(element: ${GElement}) -> Index? {
+    // FIXME: dynamic dispatch for Set and Dictionary.
+    // FIXME: _prext_indices
+    for i in indices(self) {
+      if self[i] == element {
+        return i
+      }
+    }
+    return nil
+  }
+}
+
+extension CollectionType {
+  /// Returns the first index where `predicate` returns `true` for the
+  /// corresponding value, or `nil` if such value is not found.
+  ///
+  /// Complexity: O(\ `self.count()`\ )
+  final public func _prext_find(
+    @noescape predicate: (${GElement}) -> Bool
+  ) -> Index? {
+    for i in indices(self) {
+      if predicate(self[i]) {
+        return i
+      }
+    }
+    return nil
+  }
+}
+
+//===----------------------------------------------------------------------===//
+// indices()
+//===----------------------------------------------------------------------===//
+
+extension CollectionType {
+  /// Return the range of valid index values.
+  ///
+  /// The result's `endIndex` is the same as that of `self`.  Because
+  /// `Range` is half-open, iterating the values of the result produces
+  /// all valid subscript arguments for `self`, omitting its `endIndex`.
+  final public var _prext_indices: Range<Index> {
+    return Range(start: startIndex, end: endIndex)
+  }
+}
+
--- a/stdlib/public/core/Range.swift
+++ b/stdlib/public/core/Range.swift
@@ -241,6 +241,7 @@ extension Range {
  /// Return an array containing the results of calling
  /// `transform(x)` on each element `x` of `self`.
  public func map<U>(transform: (T)->U) -> [U] {
-    return Swift.map(self, transform)
+    // FIXME(prext): remove this function when protocol extensions land.
+    return self._prext_map(transform)
  }
 }
--- a/stdlib/public/core/Reverse.swift.gyb
+++ b/stdlib/public/core/Reverse.swift.gyb
@@ -16,10 +16,10 @@
 public func reverse<C:CollectionType where C.Index: BidirectionalIndexType>(
  source: C
 ) -> [C.Generator.Element] {
-  return lazy(source).reverse().array
+  // FIXME(prext): remove this function when protocol extensions land.
+  return Array(source._prext_reverse())
 }

-
 % for traversal in ('Bidirectional', 'RandomAccess'):
 %   View = '%sReverseView' % traversal
 %   Self = 'Lazy%sCollection' % traversal
--- a/stdlib/public/core/Runtime.swift.gyb
+++ b/stdlib/public/core/Runtime.swift.gyb
@@ -252,6 +252,16 @@ public final class _stdlib_AtomicInt {
  public func addAndFetch(operand: Int) -> Int {
    return fetchAndAdd(operand) + operand
  }
+
+  public func compareExchange(inout #expected: Int, desired: Int) -> Bool {
+    var expectedVar = expected
+    let result = _stdlib_atomicCompareExchangeStrongInt(
+      object: _valuePtr,
+      expected: &expectedVar,
+      desired: desired)
+    expected = expectedVar
+    return result
+  }
 }

 //===----------------------------------------------------------------------===//
--- a/stdlib/public/core/Zip.swift
+++ b/stdlib/public/core/Zip.swift
@@ -15,7 +15,8 @@
 /// underlying sequence.
 public func zip<S0: SequenceType, S1: SequenceType>(
  s0: S0, s1: S1) -> Zip2<S0, S1> {
-  return Zip2(s0, s1)
+  // FIXME(prext): remove this function when protocol extensions land.
+  return s0._prext_zip(s1)
 }

 /// A generator for the `Zip2` sequence
@@ -37,14 +38,31 @@ public struct ZipGenerator2<
  /// since the copy was made, and no preceding call to `self.next()`
  /// has returned `nil`.
  public mutating func next() -> Element? {
+    // The next() function needs to track if it has reached the end.  If we
+    // didn't, and the first sequence is shorter than the second, then, when we
+    // have already exhausted the second sequence, on every subsequent call to
+    // next() we would consume and discard one additional element from the
+    // first sequence, even though next() return nil.
+
+    if reachedEnd {
+      return nil
+    }
+
    var e0 = baseStreams.0.next()
-    if e0 == nil { return .None }
+    if e0 == nil {
+      reachedEnd = true
+      return nil
+    }
    var e1 = baseStreams.1.next()
-    if e1 ==  nil { return .None }
+    if e1 ==  nil {
+      reachedEnd = true
+      return nil
+    }
    return .Some((e0!, e1!))
  }

  var baseStreams: (E0, E1)
+  var reachedEnd: Bool = false
 }

 /// A sequence of pairs built out of two underlying sequences, where
--- a/test/1_stdlib/Algorithm.swift
+++ b/test/1_stdlib/Algorithm.swift
@@ -1,517 +0,0 @@
-// RUN: %target-run-simple-swift
-
-import StdlibUnittest
-import SwiftPrivate
-
-var Algorithm = TestSuite("Algorithm")
-
-extension String.UnicodeScalarView : Equatable {}
-
-public func == (
-  lhs: String.UnicodeScalarView, rhs: String.UnicodeScalarView) -> Bool {
-  return Array(lhs) == Array(rhs)
-}
-
-Algorithm.test("split") {
-  expectEqual(
-    [ "foo", "  bar baz " ].map { $0.unicodeScalars },
-    split("  foo   bar baz ".unicodeScalars, maxSplit: 1) { $0._isSpace() })
-
-  expectEqual(
-    [ "foo", "bar", "baz" ].map { $0.unicodeScalars },
-    split(
-      "  foo   bar baz ".unicodeScalars, allowEmptySlices: false) { 
-      $0._isSpace() 
-    })
-
-  expectEqual(
-    [ "", "", "foo", "", "", "bar", "baz", "" ].map { $0.unicodeScalars },
-    split(
-      "  foo   bar baz ".unicodeScalars, allowEmptySlices: true) { 
-      $0._isSpace() 
-    })
-
-  expectEqual(
-    [ "", "", "foo   bar baz " ].map { $0.unicodeScalars },
-    split(
-      "  foo   bar baz ".unicodeScalars, allowEmptySlices: true, maxSplit: 2,
-      isSeparator: { $0._isSpace() }))
-}
-
-struct StartsWithTest {
-  let expected: Bool
-  let sequence: [Int]
-  let prefix: [Int]
-  let loc: SourceLoc
-
-  init(
-    _ expected: Bool, _ sequence: [Int], _ prefix: [Int],
-    file: String = __FILE__, line: UWord = __LINE__
-  ) {
-    self.expected = expected
-    self.sequence = sequence
-    self.prefix = prefix
-    self.loc = SourceLoc(file, line, comment: "test data")
-  }
-}
-
-let startsWithTests = [
-  StartsWithTest(true, [], []),
-  StartsWithTest(false, [], [ 1 ]),
-  StartsWithTest(true, [ 1 ], []),
-  StartsWithTest(true, [ 0, 1, 3, 5 ], [ 0, 1 ]),
-  StartsWithTest(true, [ 0, 1 ], [ 0, 1 ]),
-  StartsWithTest(false, [ 0, 1, 3, 5 ], [ 0, 1, 4 ]),
-  StartsWithTest(false, [ 0, 1 ], [ 0, 1, 4 ]),
-]
-
-func checkStartsWith(
-  expected: Bool, sequence: [Int], prefix: [Int],
-  stackTrace: SourceLocStack
-) {
-  expectEqual(expected, startsWith(sequence, prefix), stackTrace: stackTrace)
-  expectEqual(
-    expected, startsWith(sequence, prefix, (==)),
-    stackTrace: stackTrace)
-  expectEqual(
-    expected, startsWith(map(sequence) { $0 * 2 }, prefix) { $0 / 2 == $1 },
-    stackTrace: stackTrace)
-
-  // Test using different types for the sequence and prefix.
-  expectEqual(
-    expected, startsWith(ContiguousArray(sequence), prefix),
-    stackTrace: stackTrace)
-  expectEqual(
-    expected, startsWith(ContiguousArray(sequence), prefix, (==)),
-    stackTrace: stackTrace)
-}
-
-Algorithm.test("startsWith") {
-  for test in startsWithTests {
-    checkStartsWith(
-      test.expected, test.sequence, test.prefix, test.loc.withCurrentLoc())
-  }
-}
-
-Algorithm.test("enumerate") {
-  var result = [String]()
-  for (i, s) in enumerate( "You will never retrieve the necronomicon!"._split(" ") ) {
-    result.append("\(i) \(s)")
-  }
-  expectEqual(
-    [ "0 You", "1 will", "2 never", "3 retrieve", "4 the", "5 necronomicon!" ],
-    result)
-}
-
-Algorithm.test("equal") {
-  var _0_4 = [0, 1, 2, 3]
-  expectFalse(equal(_0_4, 0..<3))
-  expectTrue(equal(_0_4, 0..<4))
-  expectFalse(equal(_0_4, 0..<5))
-  expectFalse(equal(_0_4, 1..<4))
-}
-
-Algorithm.test("equal/predicate") {
-  func compare(lhs: (Int, Int), rhs: (Int, Int)) -> Bool {
-    return lhs.0 == rhs.0 && lhs.1 == rhs.1
-  }
-
-  var _0_4 = [(0, 10), (1, 11), (2, 12), (3, 13)]
-  expectFalse(equal(_0_4, [(0, 10), (1, 11), (2, 12)], compare))
-  expectTrue(equal(_0_4, [(0, 10), (1, 11), (2, 12), (3, 13)], compare))
-  expectFalse(equal(_0_4, [(0, 10), (1, 11), (2, 12), (3, 13), (4, 14)], compare))
-  expectFalse(equal(_0_4, [(1, 11), (2, 12), (3, 13)], compare))
-}
-
-Algorithm.test("contains") {
-  let _0_4 = [0, 1, 2, 3]
-  expectFalse(contains(_0_4, 7))
-  expectTrue(contains(_0_4, 2))
-  expectFalse(contains(_0_4, { $0 - 10 > 0  }))
-  expectTrue(contains(_0_4, { $0 % 3 == 0 }))
-}
-
-Algorithm.test("min,max") {
-  expectEqual(2, min(3, 2))
-  expectEqual(3, min(3, 7, 5))
-  expectEqual(3, max(3, 2))
-  expectEqual(7, max(3, 7, 5))
-
-  // FIXME: add tests that check that min/max return the
-  // first element of the sequence (by reference equailty) that satisfy the
-  // condition.
-}
-
-Algorithm.test("minElement,maxElement") {
-  var arr = [Int](count: 10, repeatedValue: 0)
-  for i in 0..<10 {
-    arr[i] = i % 7 + 2
-  }
-  expectEqual([2, 3, 4, 5, 6, 7, 8, 2, 3, 4], arr)
-
-  expectEqual(2, minElement(arr))
-  expectEqual(8, maxElement(arr))
-
-  // min and max element of a slice
-  expectEqual(3, minElement(arr[1..<5]))
-  expectEqual(6, maxElement(arr[1..<5]))
-
-  // FIXME: add tests that check that minElement/maxElement return the
-  // first element of the sequence (by reference equailty) that satisfy the
-  // condition.
-}
-
-Algorithm.test("filter/SequenceType") {
-  if true {
-    let s = MinimalSequence<Int>([], underestimatedCount: .Overestimate)
-    var result = filter(s) {
-      (x: Int) -> Bool in
-      expectUnreachable()
-      return true
-    }
-    expectType([Int].self, &result)
-    expectEqual([], result)
-    expectEqual([], Array(s))
-    expectEqual(0, result.capacity)
-  }
-  if true {
-    let s = MinimalSequence(
-      [ 0, 30, 10, 90 ], underestimatedCount: .Overestimate)
-    let result = filter(s) { (x: Int) -> Bool in false }
-    expectEqual([], result)
-    expectEqual([], Array(s))
-    expectEqual(0, result.capacity)
-  }
-  if true {
-    let s = MinimalSequence(
-      [ 0, 30, 10, 90 ], underestimatedCount: .Overestimate)
-    let result = filter(s) { (x: Int) -> Bool in true }
-    expectEqual([ 0, 30, 10, 90 ], result)
-    expectEqual([], Array(s))
-    expectGE(2 * result.count, result.capacity)
-  }
-  if true {
-    let s = MinimalSequence(
-      [ 0, 30, 10, 90 ], underestimatedCount: .Value(0))
-    let result = filter(s) { $0 % 3 == 0 }
-    expectEqual([ 0, 30, 90 ], result)
-    expectEqual([], Array(s))
-    expectGE(2 * result.count, result.capacity)
-  }
-  if true {
-    let s = MinimalSequence(
-      [ 0, 30, 10, 90 ], underestimatedCount: .Overestimate)
-    let result = filter(s) { $0 % 3 == 0 }
-    expectEqual([ 0, 30, 90 ], result)
-    expectEqual([], Array(s))
-    expectGE(2 * result.count, result.capacity)
-  }
-}
-
-Algorithm.test("filter/CollectionType") {
-  if true {
-    let c = MinimalForwardCollection<Int>([])
-    var result = filter(c) {
-      (x: Int) -> Bool in
-      expectUnreachable()
-      return true
-    }
-    expectEqual([], result)
-    expectType([Int].self, &result)
-    expectEqual(0, result.capacity)
-  }
-  if true {
-    let c = MinimalForwardCollection([ 0, 30, 10, 90 ])
-    let result = filter(c) { (x: Int) -> Bool in false }
-    expectEqual([], result)
-    expectEqual(0, result.capacity)
-  }
-  if true {
-    let c = MinimalForwardCollection([ 0, 30, 10, 90 ])
-    let result = filter(c) { (x: Int) -> Bool in true }
-    expectEqual([ 0, 30, 10, 90 ], result)
-    expectGE(2 * result.count, result.capacity)
-  }
-  if true {
-    let c = MinimalForwardCollection([ 0, 30, 10, 90 ])
-    let result = filter(c) { $0 % 3 == 0 }
-    expectEqual([ 0, 30, 90 ], result)
-    expectGE(2 * result.count, result.capacity)
-  }
-}
-
-Algorithm.test("filter/eager") {
-  // Make sure filter is eager and only calls its predicate once per element.
-  var count = 0
-  let one = filter(0..<10) {
-    (x: Int)->Bool in ++count; return x == 1
-  }
-  for x in one {}
-  expectEqual(10, count)
-  for x in one {}
-  expectEqual(10, count)
-}
-
-Algorithm.test("map/SequenceType") {
-  if true {
-    let s = MinimalSequence<Int>([], underestimatedCount: .Overestimate)
-    var result = map(s) {
-      (x: Int) -> Int16 in
-      expectUnreachable()
-      return 42
-    }
-    expectType([Int16].self, &result)
-    expectEqual([], result)
-    expectEqual([], Array(s))
-    // FIXME: <rdar://problem/19810841> Reserve capacity when running map() over a SequenceType
-    // expectLE(s._underestimatedCount, result.capacity)
-  }
-  if true {
-    let s = MinimalSequence(
-      [ 0, 30, 10, 90 ], underestimatedCount: .Value(0))
-    let result = map(s) { $0 + 1 }
-    expectEqual([ 1, 31, 11, 91 ], result)
-    expectEqual([], Array(s))
-    // FIXME: <rdar://problem/19810841> Reserve capacity when running map() over a SequenceType
-    // expectLE(s._underestimatedCount, result.capacity)
-  }
-  if true {
-    let s = MinimalSequence(
-      [ 0, 30, 10, 90 ], underestimatedCount: .Overestimate)
-    let result = map(s) { $0 + 1 }
-    expectEqual([ 1, 31, 11, 91 ], result)
-    expectEqual([], Array(s))
-    // FIXME: <rdar://problem/19810841> Reserve capacity when running map() over a SequenceType
-    // expectLE(s._underestimatedCount, result.capacity)
-  }
-}
-
-Algorithm.test("map/CollectionType") {
-  if true {
-    let c = MinimalForwardCollection<Int>([])
-    var result = map(c) {
-      (x: Int) -> Int16 in
-      expectUnreachable()
-      return 42
-    }
-    expectType([Int16].self, &result)
-    expectEqual([], result)
-    // FIXME: <rdar://problem/19810841> Reserve capacity when running map() over a SequenceType
-    // expectLE(c._underestimatedCount, result.capacity)
-  }
-  if true {
-    let c = MinimalForwardCollection(
-      [ 0, 30, 10, 90 ], underestimatedCount: .Value(0))
-    let result = map(c) { $0 + 1 }
-    expectEqual([ 1, 31, 11, 91 ], result)
-    // FIXME: <rdar://problem/19810841> Reserve capacity when running map() over a SequenceType
-    // expectLE(c._underestimatedCount, result.capacity)
-  }
-  if true {
-    let c = MinimalForwardCollection(
-      [ 0, 30, 10, 90 ], underestimatedCount: .Overestimate)
-    let result = map(c) { $0 + 1 }
-    expectEqual([ 1, 31, 11, 91 ], result)
-    // FIXME: <rdar://problem/19810841> Reserve capacity when running map() over a SequenceType
-    // expectLE(c._underestimatedCount, result.capacity)
-  }
-}
-
-Algorithm.test("flatMap/SequenceType") {
-  if true {
-    let s = MinimalSequence<Int>([])
-    var result = flatMap(s) {
-      (x: Int) -> [Int16] in
-      expectUnreachable()
-      return [42]
-    }
-    expectType([Int16].self, &result)
-    expectEqual([], result)
-    expectEqual([], Array(s))
-  }
-  if true {
-    let s = MinimalSequence([ 0, 30, 10, 90 ])
-    let result = flatMap(s) { [$0 + 1] }
-    expectEqual([ 1, 31, 11, 91 ], result)
-    expectEqual([], Array(s))
-  }
-}
-
-Algorithm.test("flatMap/CollectionType") {
-  if true {
-    let c = MinimalForwardCollection<Int>([])
-    var result = flatMap(c) {
-      (x: Int) -> [Int16] in
-      expectUnreachable()
-      return [42]
-    }
-    expectType([Int16].self, &result)
-    expectEqual([], result)
-  }
-  if true {
-    let c = MinimalForwardCollection([ 0, 30, 10, 90 ])
-    let result = flatMap(c) { [$0 + 1] }
-    expectEqual([ 1, 31, 11, 91 ], result)
-  }
-}
-
-Algorithm.test("sorted/strings")
-  .xfail(.LinuxAny(reason: "String comparison: ICU vs. Foundation"))
-  .code {
-  expectEqual(
-    [ "Banana", "apple", "cherry" ],
-    sorted([ "apple", "Banana", "cherry" ]))
-
-  let s = sorted(["apple", "Banana", "cherry"]) {
-    count($0) > count($1)
-  }
-  expectEqual([ "Banana", "cherry", "apple" ], s)
-}
-
-// A wrapper around Array<T> that disables any type-specific algorithm
-// optimizations and forces bounds checking on.
-struct A<T> : MutableSliceable {
-  init(_ a: Array<T>) {
-    impl = a
-  }
-
-  var startIndex: Int {
-    return 0
-  }
-
-  var endIndex: Int {
-    return impl.count
-  }
-
-  func generate() -> Array<T>.Generator {
-    return impl.generate()
-  }
-  
-  subscript(i: Int) -> T {
-    get {
-      expectTrue(i >= 0 && i < impl.count)
-      return impl[i]
-    }
-    set (x) {
-      expectTrue(i >= 0 && i < impl.count)
-      impl[i] = x
-    }
-  }
-
-  subscript(r: Range<Int>) -> Array<T>.SubSlice {
-    get {
-      expectTrue(r.startIndex >= 0 && r.startIndex <= impl.count)
-      expectTrue(r.endIndex >= 0 && r.endIndex <= impl.count)
-      return impl[r]
-    }
-    set (x) {
-      expectTrue(r.startIndex >= 0 && r.startIndex <= impl.count)
-      expectTrue(r.endIndex >= 0 && r.endIndex <= impl.count)
-      impl[r] = x
-    }
-  }
-  
-  var impl: Array<T>
-}
-
-func withInvalidOrderings(body: ((Int,Int)->Bool)->Void) {
-  // Test some ordering predicates that don't create strict weak orderings
-  body { (_,_) in true }
-  body { (_,_) in false }
-  var i = 0
-  body { (_,_) in i++ % 2 == 0 }
-  body { (_,_) in i++ % 3 == 0 }
-  body { (_,_) in i++ % 5 == 0 }
-}
-
-func randomArray() -> A<Int> {
-  let count = Int(rand32(exclusiveUpperBound: 50))
-  return A(randArray(count))
-}
-
-Algorithm.test("invalidOrderings") {
-  withInvalidOrderings {
-    var a = randomArray()
-    sort(&a, $0)
-  }
-  withInvalidOrderings {
-    var a: A<Int>
-    a = randomArray()
-    partition(&a, indices(a), $0)
-  }
-  /*
-  // FIXME: Disabled due to <rdar://problem/17734737> Unimplemented:
-  // abstraction difference in l-value
-  withInvalidOrderings {
-    var a = randomArray()
-    var pred = $0
-    _insertionSort(&a, indices(a), &pred)
-  }
-  */
-  withInvalidOrderings {
-    let predicate: (Int,Int)->Bool = $0
-    let result = lexicographicalCompare(randomArray(), randomArray(), isOrderedBefore: predicate)
-  }
-}
-
-// The routine is based on http://www.cs.dartmouth.edu/~doug/mdmspe.pdf
-func makeQSortKiller(len: Int) -> [Int] {
-  var candidate: Int = 0
-  var keys = [Int:Int]()
-  func Compare(x: Int, y : Int) -> Bool {
-    if keys[x] == nil && keys[y] == nil {
-      if (x == candidate) {
-        keys[x] = keys.count
-      } else {
-        keys[y] = keys.count
-      }
-    }
-    if keys[x] == nil {
-      candidate = x
-      return true
-    }
-    if keys[y] == nil {
-      candidate = y
-      return false
-    }
-    return keys[x]! > keys[y]!
-  }
-
-  var ary = [Int](count: len, repeatedValue:0)
-  var ret = [Int](count: len, repeatedValue:0)
-  for i in 0..<len { ary[i] = i }
-  ary = sorted(ary, Compare)
-  for i in 0..<len {
-    ret[ary[i]] = i
-  }
-  return ret
-}
-
-Algorithm.test("sorted/complexity") {
-  var ary: [Int] = []
-
-  // Check performance of sort on array of repeating values
-  var comparisons_100 = 0
-  ary = [Int](count: 100, repeatedValue: 0)
-  sort(&ary) { comparisons_100++; return $0 < $1 }
-  var comparisons_1000 = 0
-  ary = [Int](count: 1000, repeatedValue: 0)
-  sort(&ary) { comparisons_1000++; return $0 < $1 }
-  expectTrue(comparisons_1000/comparisons_100 < 20)
-
-  // Try to construct 'bad' case for quicksort, on which the algorithm
-  // goes quadratic.
-  comparisons_100 = 0
-  ary = makeQSortKiller(100)
-  sort(&ary) { comparisons_100++; return $0 < $1 }
-  comparisons_1000 = 0
-  ary = makeQSortKiller(1000)
-  sort(&ary) { comparisons_1000++; return $0 < $1 }
-  expectTrue(comparisons_1000/comparisons_100 < 20)
-}
-
-Algorithm.test("sorted/return type") {
-  let x: Array = sorted([5, 4, 3, 2, 1] as ArraySlice)
-}
-runAllTests()
-
--- a/test/1_stdlib/Algorithm.swift.gyb
+++ b/test/1_stdlib/Algorithm.swift.gyb
--- a/test/1_stdlib/Reverse.swift
+++ b/test/1_stdlib/Reverse.swift
@@ -11,6 +11,8 @@
 //===----------------------------------------------------------------------===//
 // RUN: %target-run-simple-swift | FileCheck %s

+// FIXME(prext): remove this file when protocol extensions land.
+
 // CHECK: testing...
 println("testing...")

--- a/test/1_stdlib/Zip.swift
+++ b/test/1_stdlib/Zip.swift
@@ -1,5 +1,7 @@
 // RUN: %target-run-simple-swift | FileCheck %s

+// FIXME(prext): remove this file when protocol extensions land.
+
 var n = [2, 3, 5, 7, 11]
 var s = ["two", "three", "five", "seven", "eleven", "thirteen"]

--- a/test/Constraints/generic_protocol_witness.swift
+++ b/test/Constraints/generic_protocol_witness.swift
@@ -56,7 +56,7 @@ func usesAGenericMethod<U : NeedsAGenericMethod>(x: U) {
  x.method(5)
 }

-struct L<T>: SequenceType {} // expected-error {{type 'L<T>' does not conform to protocol '_Sequence_Type'}} expected-error {{type 'L<T>' does not conform to protocol 'SequenceType'}}
+struct L<T>: SequenceType {} // expected-error {{type 'L<T>' does not conform to protocol '_Sequence_Type'}} expected-error {{type 'L<T>' does not conform to protocol 'SequenceType'}} expected-error {{type 'L<T>' does not conform to protocol '_SequenceDefaultsType'}}

 func z(x: L<Int>) {
  for xx in x {} // expected-error{{'L<Int>' does not have a member named 'Generator'}}
--- a/test/IDE/complete_from_stdlib.swift
+++ b/test/IDE/complete_from_stdlib.swift
@@ -6,10 +6,6 @@
 // RUN: FileCheck %s -check-prefix=PRIVATE_NOMINAL_MEMBERS_1 < %t.members.txt
 // RUN: FileCheck %s -check-prefix=NO_STDLIB_PRIVATE < %t.members.txt

-// RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=PRIVATE_PROTOCOL_MEMBERS_1 > %t.protocol.members.txt
-// RUN: FileCheck %s -check-prefix=PRIVATE_PROTOCOL_MEMBERS_1 < %t.protocol.members.txt
-// RUN: FileCheck %s -check-prefix=NO_STDLIB_PRIVATE < %t.protocol.members.txt
-
 // NO_STDLIB_PRIVATE: Begin completions
 // NO_STDLIB_PRIVATE-NOT: Decl[{{.*}}]{{[^:]*}}: _
 // NO_STDLIB_PRIVATE: End completions
@@ -28,11 +24,3 @@ func privateNominalMembers(a: String) {
 // PRIVATE_NOMINAL_MEMBERS_1-DAG: Decl[InstanceVar]/CurrNominal: startIndex[#String.Index#]{{; name=.+$}}
 // PRIVATE_NOMINAL_MEMBERS_1: End completions

-func privateProtocolMembers(a: CollectionType) {
-  a.#^PRIVATE_PROTOCOL_MEMBERS_1^#
-}
-
-// PRIVATE_PROTOCOL_MEMBERS_1: Begin completions
-// PRIVATE_PROTOCOL_MEMBERS_1-DAG: Decl[InstanceVar]/Super: startIndex[#Self.Index#]
-
-// PRIVATE_PROTOCOL_MEMBERS_1: End completions
--- a/test/stmt/foreach.swift
+++ b/test/stmt/foreach.swift
@@ -8,16 +8,16 @@ func bad_containers_1(bc: BadContainer1) {
  for e in bc { } // expected-error{{type 'BadContainer1' does not conform to protocol 'SequenceType'}}
 }

-struct BadContainer2 : SequenceType { // expected-error{{type 'BadContainer2' does not conform to protocol '_Sequence_Type'}} expected-error{{type 'BadContainer2' does not conform to protocol 'SequenceType'}}
-  var generate : Int // expected-note{{candidate is not a function}} expected-note{{candidate is not a function}}
+struct BadContainer2 : SequenceType { // expected-error{{type 'BadContainer2' does not conform to protocol '_Sequence_Type'}} expected-error{{type 'BadContainer2' does not conform to protocol 'SequenceType'}} expected-error{{type 'BadContainer2' does not conform to protocol '_SequenceDefaultsType'}}
+  var generate : Int // expected-note 3{{candidate is not a function}}
 }

 func bad_containers_2(bc: BadContainer2) {
  for e in bc { } // expected-error{{'BadContainer2' does not have a member named 'Generator'}}
 }

-struct BadContainer3 : SequenceType { // expected-error{{type 'BadContainer3' does not conform to protocol '_Sequence_Type'}} expected-error{{type 'BadContainer3' does not conform to protocol 'SequenceType'}} 
-  func generate() { } // expected-note{{candidate has non-matching type '() -> ()'}} expected-note{{candidate has non-matching type '() -> ()'}}
+struct BadContainer3 : SequenceType { // expected-error{{type 'BadContainer3' does not conform to protocol '_Sequence_Type'}} expected-error{{type 'BadContainer3' does not conform to protocol 'SequenceType'}} expected-error{{type 'BadContainer3' does not conform to protocol '_SequenceDefaultsType'}}
+  func generate() { } // expected-note 3{{candidate has non-matching type '() -> ()'}}
 }

 func bad_containers_3(bc: BadContainer3) {
@@ -28,8 +28,8 @@ struct BadGeneratorType1 {
  
 }

-struct BadContainer4 : SequenceType { // expected-error{{type 'BadContainer4' does not conform to protocol '_Sequence_Type'}} expected-error{{type 'BadContainer4' does not conform to protocol 'SequenceType'}}
-  typealias Generator = BadGeneratorType1 // expected-note{{possibly intended match 'Generator' does not conform to 'GeneratorType'}} expected-note{{possibly intended match 'Generator' does not conform to 'GeneratorType'}}
+struct BadContainer4 : SequenceType { // expected-error{{type 'BadContainer4' does not conform to protocol '_Sequence_Type'}} expected-error{{type 'BadContainer4' does not conform to protocol 'SequenceType'}} expected-error{{type 'BadContainer4' does not conform to protocol '_SequenceDefaultsType'}}
+  typealias Generator = BadGeneratorType1 // expected-note 3{{possibly intended match 'Generator' does not conform to 'GeneratorType'}}
  func generate() -> BadGeneratorType1 { }
 }

--- a/validation-test/stdlib/Concatenate.swift
+++ b/validation-test/stdlib/Concatenate.swift
@@ -32,13 +32,13 @@ let expected = ContiguousArray(0..<8)

 for (expected, source) in samples {
  ConcatenateTests.test("forward-\(source)") {
-    checkCollection(
+    checkBidirectionalCollection(
      expected,
      _lazyConcatenate(source),
      SourceLocStack().withCurrentLoc())
  }
  ConcatenateTests.test("reverse-\(source)") {
-    checkCollection(
+    checkBidirectionalCollection(
      ContiguousArray(lazy(expected).reverse()),
      _lazyConcatenate(source).reverse(),
      SourceLocStack().withCurrentLoc())
--- a/validation-test/stdlib/CoreAudio.swift
+++ b/validation-test/stdlib/CoreAudio.swift
@@ -253,7 +253,8 @@ CoreAudioTestSuite.test("UnsafeMutableAudioBufferListPointer.subscript(_: Int)/t
 }

 CoreAudioTestSuite.test("UnsafeMutableAudioBufferListPointer/Collection") {
-  let ablPtrWrapper = AudioBufferList.allocate(maximumBuffers: 16)
+  var ablPtrWrapper = AudioBufferList.allocate(maximumBuffers: 16)
+  expectType(UnsafeMutableAudioBufferListPointer.self, &ablPtrWrapper)

  var expected: [AudioBuffer] = []
  for i in 0..<16 {
@@ -265,7 +266,9 @@ CoreAudioTestSuite.test("UnsafeMutableAudioBufferListPointer/Collection") {
    expected.append(audioBuffer)
  }

-  checkCollection(expected, ablPtrWrapper, SourceLocStack().withCurrentLoc())
+  // FIXME: use checkMutableRandomAccessCollection, when we have that function.
+  checkRandomAccessCollection(
+    expected, ablPtrWrapper, SourceLocStack().withCurrentLoc())
  free(ablPtrWrapper.unsafeMutablePointer)
 }

--- a/validation-test/stdlib/Unicode.swift
+++ b/validation-test/stdlib/Unicode.swift
@@ -2168,7 +2168,9 @@ class NonContiguousNSString : NSString {

 func checkUTF8View(expected: [UInt8], subject: String,
    stackTrace: SourceLocStack) {
-  checkCollection(expected, subject.utf8, stackTrace.withCurrentLoc())
+  checkForwardCollection(
+    expected, subject.utf8,
+    stackTrace.withCurrentLoc())
 }

 func checkUTF16View(expected: [UInt16], subject: String,