stdlib/public/core/MigrationSupport.swift

//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2018 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

// This file contains only support for types deprecated from previous versions
// of Swift

@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "BidirectionalCollection")
public typealias BidirectionalIndexable = BidirectionalCollection
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "Collection")
public typealias IndexableBase = Collection
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "Collection")
public typealias Indexable = Collection
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "MutableCollection")
public typealias MutableIndexable = MutableCollection
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "RandomAccessCollection")
public typealias RandomAccessIndexable = RandomAccessCollection
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "RangeReplaceableIndexable")
public typealias RangeReplaceableIndexable = RangeReplaceableCollection
@available(swift, deprecated: 4.2, renamed: "EnumeratedSequence.Iterator")
public typealias EnumeratedIterator<T: Sequence> = EnumeratedSequence<T>.Iterator
@available(swift,deprecated: 4.2, obsoleted: 5.0, renamed: "CollectionOfOne.Iterator")
public typealias IteratorOverOne<T> = CollectionOfOne<T>.Iterator
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "EmptyCollection.Iterator")
public typealias EmptyIterator<T> = EmptyCollection<T>.Iterator
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "LazyFilterSequence.Iterator")
public typealias LazyFilterIterator<T: Sequence> = LazyFilterSequence<T>.Iterator
@available(swift, deprecated: 3.1, obsoleted: 5.0, message: "Use Base.Index")
public typealias LazyFilterIndex<Base: Collection> = Base.Index
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "LazyDropWhileSequence.Iterator")
public typealias LazyDropWhileIterator<T> = LazyDropWhileSequence<T>.Iterator where T: Sequence
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "LazyDropWhileCollection.Index")
public typealias LazyDropWhileIndex<T> = LazyDropWhileCollection<T>.Index where T: Collection
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "LazyDropWhileCollection")
public typealias LazyDropWhileBidirectionalCollection<T> = LazyDropWhileCollection<T> where T: BidirectionalCollection
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "LazyFilterCollection")
public typealias LazyFilterBidirectionalCollection<T> = LazyFilterCollection<T> where T : BidirectionalCollection
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "LazyMapSequence.Iterator")
public typealias LazyMapIterator<T, E> = LazyMapSequence<T, E>.Iterator where T: Sequence
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "LazyMapCollection")
public typealias LazyMapBidirectionalCollection<T, E> = LazyMapCollection<T, E> where T : BidirectionalCollection
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "LazyMapCollection")
public typealias LazyMapRandomAccessCollection<T, E> = LazyMapCollection<T, E> where T : RandomAccessCollection
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "LazyCollection")
public typealias LazyBidirectionalCollection<T> = LazyCollection<T> where T : BidirectionalCollection
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "LazyCollection")
public typealias LazyRandomAccessCollection<T> = LazyCollection<T> where T : RandomAccessCollection
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "FlattenCollection.Index")
public typealias FlattenCollectionIndex<T> = FlattenCollection<T>.Index where T : Collection, T.Element : Collection
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "FlattenCollection.Index")
public typealias FlattenBidirectionalCollectionIndex<T> = FlattenCollection<T>.Index where T : BidirectionalCollection, T.Element : BidirectionalCollection
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "FlattenCollection")
public typealias FlattenBidirectionalCollection<T> = FlattenCollection<T> where T : BidirectionalCollection, T.Element : BidirectionalCollection
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "JoinedSequence.Iterator")
public typealias JoinedIterator<T: Sequence> = JoinedSequence<T>.Iterator where T.Element: Sequence
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "Zip2Sequence.Iterator")
public typealias Zip2Iterator<T, U> = Zip2Sequence<T, U>.Iterator where T: Sequence, U: Sequence
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "LazyDropWhileSequence.Iterator")
public typealias LazyPrefixWhileIterator<T> = LazyPrefixWhileSequence<T>.Iterator where T: Sequence
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "LazyDropWhileCollection.Index")
public typealias LazyPrefixWhileIndex<T> = LazyPrefixWhileCollection<T>.Index where T: Collection
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "LazyPrefixWhileCollection")
public typealias LazyPrefixWhileBidirectionalCollection<T> = LazyPrefixWhileCollection<T> where T: BidirectionalCollection
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "ReversedCollection")
public typealias ReversedRandomAccessCollection<T: RandomAccessCollection> = ReversedCollection<T>
@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "ReversedCollection.Index")
public typealias ReversedIndex<T: BidirectionalCollection> = ReversedCollection<T>
@available(swift, deprecated: 4.0, obsoleted: 5.0, renamed: "Slice")
public typealias BidirectionalSlice<T> = Slice<T> where T : BidirectionalCollection
@available(swift, deprecated: 4.0, obsoleted: 5.0, renamed: "Slice")
public typealias RandomAccessSlice<T> = Slice<T> where T : RandomAccessCollection
@available(swift, deprecated: 4.0, obsoleted: 5.0, renamed: "Slice")
public typealias RangeReplaceableSlice<T> = Slice<T> where T : RangeReplaceableCollection
@available(swift, deprecated: 4.0, obsoleted: 5.0, renamed: "Slice")
public typealias RangeReplaceableBidirectionalSlice<T> = Slice<T> where T : RangeReplaceableCollection & BidirectionalCollection
@available(swift, deprecated: 4.0, obsoleted: 5.0, renamed: "Slice")
public typealias RangeReplaceableRandomAccessSlice<T> = Slice<T> where T : RangeReplaceableCollection & RandomAccessCollection
@available(swift, deprecated: 4.0, obsoleted: 5.0, renamed: "Slice")
public typealias MutableSlice<T> = Slice<T> where T : MutableCollection
@available(swift, deprecated: 4.0, obsoleted: 5.0, renamed: "Slice")
public typealias MutableBidirectionalSlice<T> = Slice<T> where T : MutableCollection & BidirectionalCollection
@available(swift, deprecated: 4.0, obsoleted: 5.0, renamed: "Slice")
public typealias MutableRandomAccessSlice<T> = Slice<T> where T : MutableCollection & RandomAccessCollection
@available(swift, deprecated: 4.0, obsoleted: 5.0, renamed: "Slice")
public typealias MutableRangeReplaceableSlice<T> = Slice<T> where T : MutableCollection & RangeReplaceableCollection
@available(swift, deprecated: 4.0, obsoleted: 5.0, renamed: "Slice")
public typealias MutableRangeReplaceableBidirectionalSlice<T> = Slice<T> where T : MutableCollection & RangeReplaceableCollection & BidirectionalCollection
@available(swift, deprecated: 4.0, obsoleted: 5.0, renamed: "Slice")
public typealias MutableRangeReplaceableRandomAccessSlice<T> = Slice<T> where T : MutableCollection & RangeReplaceableCollection & RandomAccessCollection
@available(swift, deprecated: 4.0, obsoleted: 5.0, renamed: "DefaultIndices")
public typealias DefaultBidirectionalIndices<T> = DefaultIndices<T> where T : BidirectionalCollection
@available(swift, deprecated: 4.0, obsoleted: 5.0, renamed: "DefaultIndices")
public typealias DefaultRandomAccessIndices<T> = DefaultIndices<T> where T : RandomAccessCollection

// Deprecated by SE-0115.
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "ExpressibleByNilLiteral")
public typealias NilLiteralConvertible = ExpressibleByNilLiteral
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "_ExpressibleByBuiltinIntegerLiteral")
public typealias _BuiltinIntegerLiteralConvertible = _ExpressibleByBuiltinIntegerLiteral
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "ExpressibleByIntegerLiteral")
public typealias IntegerLiteralConvertible = ExpressibleByIntegerLiteral
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "_ExpressibleByBuiltinFloatLiteral")
public typealias _BuiltinFloatLiteralConvertible = _ExpressibleByBuiltinFloatLiteral
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "ExpressibleByFloatLiteral")
public typealias FloatLiteralConvertible = ExpressibleByFloatLiteral
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "_ExpressibleByBuiltinBooleanLiteral")
public typealias _BuiltinBooleanLiteralConvertible = _ExpressibleByBuiltinBooleanLiteral
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "ExpressibleByBooleanLiteral")
public typealias BooleanLiteralConvertible = ExpressibleByBooleanLiteral
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "_ExpressibleByBuiltinUnicodeScalarLiteral")
public typealias _BuiltinUnicodeScalarLiteralConvertible = _ExpressibleByBuiltinUnicodeScalarLiteral
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "ExpressibleByUnicodeScalarLiteral")
public typealias UnicodeScalarLiteralConvertible = ExpressibleByUnicodeScalarLiteral
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "_ExpressibleByBuiltinExtendedGraphemeClusterLiteral")
public typealias _BuiltinExtendedGraphemeClusterLiteralConvertible = _ExpressibleByBuiltinExtendedGraphemeClusterLiteral
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "ExpressibleByExtendedGraphemeClusterLiteral")
public typealias ExtendedGraphemeClusterLiteralConvertible = ExpressibleByExtendedGraphemeClusterLiteral
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "_ExpressibleByBuiltinStringLiteral")
public typealias _BuiltinStringLiteralConvertible = _ExpressibleByBuiltinStringLiteral
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "_ExpressibleByBuiltinUTF16StringLiteral")
public typealias _BuiltinUTF16StringLiteralConvertible = _ExpressibleByBuiltinUTF16StringLiteral
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "ExpressibleByStringLiteral")
public typealias StringLiteralConvertible = ExpressibleByStringLiteral
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "ExpressibleByArrayLiteral")
public typealias ArrayLiteralConvertible = ExpressibleByArrayLiteral
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "ExpressibleByDictionaryLiteral")
public typealias DictionaryLiteralConvertible = ExpressibleByDictionaryLiteral
@available(swift, deprecated: 3.0, obsoleted: 5.0, message: "it will be replaced or redesigned in Swift 4.0.  Instead of conforming to 'StringInterpolationConvertible', consider adding an 'init(_:String)'")
public typealias StringInterpolationConvertible = ExpressibleByStringInterpolation
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "_ExpressibleByColorLiteral")
public typealias _ColorLiteralConvertible = _ExpressibleByColorLiteral
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "_ExpressibleByImageLiteral")
public typealias _ImageLiteralConvertible = _ExpressibleByImageLiteral
@available(swift, deprecated: 3.0, obsoleted: 5.0, renamed: "_ExpressibleByFileReferenceLiteral")
public typealias _FileReferenceLiteralConvertible = _ExpressibleByFileReferenceLiteral

@available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "ClosedRange.Index")
public typealias ClosedRangeIndex<T> = ClosedRange<T>.Index where T: Strideable, T.Stride: SignedInteger

/// An optional type that allows implicit member access.
///
/// The `ImplicitlyUnwrappedOptional` type is deprecated. To create an optional
/// value that is implicitly unwrapped, place an exclamation mark (`!`) after
/// the type that you want to denote as optional.
///
///     // An implicitly unwrapped optional integer
///     let guaranteedNumber: Int! = 6
///
///     // An optional integer
///     let possibleNumber: Int? = 5
@available(*, unavailable, renamed: "Optional")
public typealias ImplicitlyUnwrappedOptional<Wrapped> = Optional<Wrapped>

@available(swift, deprecated: 3.1, obsoleted: 4.0, message: "Use FixedWidthInteger protocol instead")
public typealias BitwiseOperations = _BitwiseOperations

public protocol _BitwiseOperations {
  static func & (lhs: Self, rhs: Self) -> Self
  static func | (lhs: Self, rhs: Self) -> Self
  static func ^ (lhs: Self, rhs: Self) -> Self
  static prefix func ~ (x: Self) -> Self
  static var allZeros: Self { get }
}

extension _BitwiseOperations {  
    @available(swift, obsoleted: 4.1)
    public static func |= (lhs: inout Self, rhs: Self) {
      lhs = lhs | rhs
    }

    @available(swift, obsoleted: 4.1)
    public static func &= (lhs: inout Self, rhs: Self) {
      lhs = lhs & rhs
    }

    @available(swift, obsoleted: 4.1)
    public static func ^= (lhs: inout Self, rhs: Self) {
      lhs = lhs ^ rhs
    }
}

extension FloatingPoint {
  @available(swift, obsoleted: 4, message: "Please use operators instead.")
  public func negated() -> Self {
    return -self
  }

  @available(swift, obsoleted: 4, message: "Please use operators instead.")
  public func adding(_ other: Self) -> Self {
    return self + other
  }

  @available(swift, obsoleted: 4, message: "Please use operators instead.")
  public mutating func add(_ other: Self) {
    self += other
  }

  @available(swift, obsoleted: 4, message: "Please use operators instead.")
  public func subtracting(_ other: Self) -> Self {
    return self - other
  }

  @available(swift, obsoleted: 4, message: "Please use operators instead.")
  public mutating func subtract(_ other: Self) {
    self -= other
  }

  @available(swift, obsoleted: 4, message: "Please use operators instead.")
  public func multiplied(by other: Self) -> Self {
    return self * other
  }

  @available(swift, obsoleted: 4, message: "Please use operators instead.")
  public mutating func multiply(by other: Self) {
    self *= other
  }

  @available(swift, obsoleted: 4, message: "Please use operators instead.")
  public func divided(by other: Self) -> Self {
    return self / other
  }

  @available(swift, obsoleted: 4, message: "Please use operators instead.")
  public mutating func divide(by other: Self) {
    self /= other
  }
}

extension FloatingPoint {
  @available(*, unavailable, message: "Use bitPattern property instead")
  public func _toBitPattern() -> UInt {
    fatalError("unavailable")
  }

  @available(*, unavailable, message: "Use init(bitPattern:) instead")
  public static func _fromBitPattern(_ bits: UInt) -> Self {
    fatalError("unavailable")
  }
}

extension BinaryFloatingPoint {
  @available(*, unavailable, renamed: "isSignalingNaN")
  public var isSignaling: Bool {
    fatalError("unavailable")
  }

  @available(*, unavailable, renamed: "nan")
  public var NaN: Bool {
    fatalError("unavailable")
  }
  @available(*, unavailable, renamed: "nan")
  public var quietNaN: Bool {
    fatalError("unavailable")
  }
}

@available(*, unavailable, renamed: "FloatingPoint")
public typealias FloatingPointType = FloatingPoint

// Swift 3 compatibility APIs
@available(swift, obsoleted: 4, renamed: "BinaryInteger")
public typealias Integer = BinaryInteger

@available(swift, obsoleted: 4, renamed: "BinaryInteger")
public typealias IntegerArithmetic = BinaryInteger

@available(swift, obsoleted: 4, message: "Please use 'SignedNumeric & Comparable' instead.")
public typealias SignedNumber = SignedNumeric & Comparable

@available(swift, obsoleted: 4, message: "Please use 'SignedNumeric & Comparable' instead.")
public typealias AbsoluteValuable = SignedNumeric & Comparable

@available(swift, obsoleted: 4, renamed: "SignedInteger")
public typealias _SignedInteger = SignedInteger

extension SignedNumeric where Self : Comparable {
  @available(swift, obsoleted: 4, message: "Please use the 'abs(_:)' free function.")
  @_transparent
  public static func abs(_ x: Self) -> Self {
    return Swift.abs(x)
  }
}

extension BinaryInteger {
  @available(swift, obsoleted: 4)
  public func toIntMax() -> Int64 {
    return Int64(self)
  }
}

extension UnsignedInteger {
  @available(swift, obsoleted: 4)
  public func toUIntMax() -> UInt64 {
    return UInt64(self)
  }
}

extension Range where Bound: Strideable, Bound.Stride : SignedInteger {
  /// Now that Range is conditionally a collection when Bound: Strideable,
  /// CountableRange is no longer needed. This is a deprecated initializer
  /// for any remaining uses of Range(countableRange).
  @available(swift, deprecated: 4.2, obsoleted: 5.0, message: "CountableRange is now a Range. No need to convert any more.")
  public init(_ other: Range<Bound>) {
    self = other
  }  
}

extension ClosedRange where Bound: Strideable, Bound.Stride : SignedInteger {
  /// Now that Range is conditionally a collection when Bound: Strideable,
  /// CountableRange is no longer needed. This is a deprecated initializer
  /// for any remaining uses of Range(countableRange).
  @available(swift, deprecated: 4.2, obsoleted: 5.0, message: "CountableClosedRange is now a ClosedRange. No need to convert any more.")
  public init(_ other: ClosedRange<Bound>) {
    self = other
  }  
}

extension _ExpressibleByColorLiteral {
  @available(swift, deprecated: 3.2, obsoleted: 4.0, message: "This initializer is only meant to be used by color literals")
  public init(colorLiteralRed red: Float, green: Float, blue: Float, alpha: Float) {
    self.init(_colorLiteralRed: red, green: green, blue: blue, alpha: alpha)
  }
}

@available(swift, deprecated: 5.0, renamed: "KeyValuePairs")
public typealias DictionaryLiteral<Key, Value> = KeyValuePairs<Key, Value>

extension LazySequenceProtocol {
  /// Returns the non-`nil` results of mapping the given transformation over
  /// this sequence.
  ///
  /// Use this method to receive a sequence of nonoptional values when your
  /// transformation produces an optional value.
  ///
  /// - Parameter transform: A closure that accepts an element of this sequence
  ///   as its argument and returns an optional value.
  ///
  /// - Complexity: O(1)
  @available(swift, deprecated: 4.1, renamed: "compactMap(_:)", message: "Please use compactMap(_:) for the case where closure returns an optional value")
  public func flatMap<ElementOfResult>(
    _ transform: @escaping (Elements.Element) -> ElementOfResult?
  ) -> LazyMapSequence<
    LazyFilterSequence<
      LazyMapSequence<Elements, ElementOfResult?>>,
    ElementOfResult
  > {
    return self.compactMap(transform)
  }
}

extension LazyMapCollection {
  // This overload is needed to re-enable Swift 3 source compatibility related
  // to a bugfix in ranking behavior of the constraint solver.
  @available(swift, obsoleted: 4.0)
  public static func + <
    Other : LazyCollectionProtocol
  >(lhs: LazyMapCollection, rhs: Other) -> [Element]
  where Other.Element == Element {
    var result: [Element] = []
    result.reserveCapacity(numericCast(lhs.count + rhs.count))
    result.append(contentsOf: lhs)
    result.append(contentsOf: rhs)
    return result
  }
}

extension FloatingPoint {
  @available(swift, deprecated: 3.1, obsoleted: 4.0, message: "Please use the `abs(_:)` free function")
  public static func abs(_ x: Self) -> Self {
    return x.magnitude
  }
}

extension FixedWidthInteger {
  /// The empty bitset.
  @available(swift, deprecated: 3.1, obsoleted: 4.0, message: "Use 0")
  public static var allZeros: Self { return 0 }
}

extension LazyCollectionProtocol {
  /// Returns the non-`nil` results of mapping the given transformation over
  /// this collection.
  ///
  /// Use this method to receive a collection of nonoptional values when your
  /// transformation produces an optional value.
  ///
  /// - Parameter transform: A closure that accepts an element of this
  ///   collection as its argument and returns an optional value.
  ///
  /// - Complexity: O(1)
  @available(swift, deprecated: 4.1, obsoleted: 5.0, renamed: "compactMap(_:)",
    message: "Please use compactMap(_:) for the case where closure returns an optional value")
  public func flatMap<ElementOfResult>(
    _ transform: @escaping (Elements.Element) -> ElementOfResult?
  ) -> LazyMapCollection<
    LazyFilterCollection<
      LazyMapCollection<Elements, ElementOfResult?>>,
    ElementOfResult
  > {
    return self.map(transform).filter { $0 != nil }.map { $0! }
  }
}

extension String {
  /// A view of a string's contents as a collection of characters.
  ///
  /// Previous versions of Swift provided this view since String
  /// itself was not a collection. String is now a collection of
  /// characters, so this type is now just an alias for String.
  @available(swift, deprecated: 3.2, obsoleted: 5.0, message: "Please use String directly")
  public typealias CharacterView = String

  /// A view of the string's contents as a collection of characters.
  ///
  /// Previous versions of Swift provided this view since String
  /// itself was not a collection. String is now a collection of
  /// characters, so this type is now just an alias for String.
  @available(swift, deprecated: 3.2, obsoleted: 5.0, message: "Please use String directly")
  public var characters: String {
    get {
      return self
    }
    set {
      self = newValue
    }
  }

  /// Applies the given closure to a mutable view of the string's characters.
  ///
  /// Previous versions of Swift provided this view since String
  /// itself was not a collection. String is now a collection of
  /// characters, so this type is now just an alias for String.
  @available(swift, deprecated: 3.2, obsoleted: 5.0, message: "Please mutate the String directly")
  public mutating func withMutableCharacters<R>(
    _ body: (inout String) -> R
  ) -> R {
    return body(&self)
  }

  @available(swift, deprecated: 3.2, obsoleted: 4.0)
  public init?(_ utf16: UTF16View) {
    Builtin.unreachable()
  }

  @available(swift, deprecated: 3.2, message: "Failable initializer was removed in Swift 4. When upgrading to Swift 4, please use non-failable String.init(_:UTF8View)")
  @available(swift, obsoleted: 4.0, message: "Please use non-failable String.init(_:UTF8View) instead")
  public init?(_ utf8: UTF8View) {
    Builtin.unreachable()
  }
}

extension String { // RangeReplaceableCollection
  // The defaulted argument prevents this initializer from satisfies the
  // LosslessStringConvertible conformance.  You can satisfy a protocol
  // requirement with something that's not yet available, but not with
  // something that has become unavailable. Without this, the code won't
  // compile as Swift 4.
  @available(swift, obsoleted: 4, message: "String.init(_:String) is no longer failable")
  public init?(_ other: String, obsoletedInSwift4: () = ()) {
    Builtin.unreachable()
  }
}

@available(*, unavailable, renamed: "TextOutputStream")
public typealias OutputStreamType = TextOutputStream

extension TextOutputStreamable {
  @available(*, unavailable, renamed: "write(to:)")
  public func writeTo<Target : TextOutputStream>(_ target: inout Target) {
    Builtin.unreachable()
  }
}


extension String.UnicodeScalarView : _CustomPlaygroundQuickLookable {
  @available(swift, deprecated: 4.2/*, obsoleted: 5.0*/, message: "UnicodeScalarView.customPlaygroundQuickLook will be removed in Swift 5.0")
  public var customPlaygroundQuickLook: _PlaygroundQuickLook {
    return .text(description)
  }
}

// backward compatibility for index interchange.
extension String.UnicodeScalarView {
  @available(swift, obsoleted: 4.0, message: "Any String view index conversion can fail in Swift 4; please unwrap the optional index")
  public func index(after i: Index?) -> Index {
    Builtin.unreachable()
  }
  @available(swift, obsoleted: 4.0, message: "Any String view index conversion can fail in Swift 4; please unwrap the optional index")
  public func index(_ i: Index?,  offsetBy n: Int) -> Index {
    Builtin.unreachable()
  }
  @available(swift, obsoleted: 4.0, message: "Any String view index conversion can fail in Swift 4; please unwrap the optional indices")
  public func distance(from i: Index?, to j: Index?) -> Int {
    Builtin.unreachable()
  }
  @available(swift, obsoleted: 4.0, message: "Any String view index conversion can fail in Swift 4; please unwrap the optional index")
  public subscript(i: Index?) -> Unicode.Scalar {
    Builtin.unreachable()
  }
}

// backward compatibility for index interchange.
extension String.UTF16View {
  @available(swift, obsoleted: 4.0, message: "Any String view index conversion can fail in Swift 4; please unwrap the optional index")
  public func index(after i: Index?) -> Index {
    Builtin.unreachable()
  }
  @available(swift, obsoleted: 4.0, message: "Any String view index conversion can fail in Swift 4; please unwrap the optional index")
  public func index(_ i: Index?, offsetBy n: Int) -> Index {
    Builtin.unreachable()
  }
  @available(swift, obsoleted: 4.0, message: "Any String view index conversion can fail in Swift 4; please unwrap the optional indices")
  public func distance(from i: Index?, to j: Index?) -> Int {
    Builtin.unreachable()
  }
  @available(swift, obsoleted: 4.0, message: "Any String view index conversion can fail in Swift 4; please unwrap the optional index")
  public subscript(i: Index?) -> Unicode.UTF16.CodeUnit {
    Builtin.unreachable()
  }
}

// backward compatibility for index interchange.
extension String.UTF8View {
  @available(swift, obsoleted: 4.0, message: "Any String view index conversion can fail in Swift 4; please unwrap the optional index")
  public func index(after i: Index?) -> Index {
    Builtin.unreachable()
  }
  @available(swift, obsoleted: 4.0, message: "Any String view index conversion can fail in Swift 4; please unwrap the optional index")
  public func index(_ i: Index?, offsetBy n: Int) -> Index {
    Builtin.unreachable()
  }
  @available(swift, obsoleted: 4.0, message: "Any String view index conversion can fail in Swift 4; please unwrap the optional indices")
  public func distance(from i: Index?, to j: Index?) -> Int {
    Builtin.unreachable()
  }
  @available(swift, obsoleted: 4.0, message: "Any String view index conversion can fail in Swift 4; please unwrap the optional index")
  public subscript(i: Index?) -> Unicode.UTF8.CodeUnit {
    Builtin.unreachable()
  }
}

//===--- String/Substring Slicing Support ---------------------------------===//
/// In Swift 3.2, in the absence of type context,
///
///     someString[someString.startIndex..<someString.endIndex]
///
/// was deduced to be of type `String`.  Therefore have a more-specific
/// Swift-3-only `subscript` overload on `String` (and `Substring`) that
/// continues to produce `String`.
extension String {
  @available(swift, obsoleted: 4)
  public subscript(bounds: Range<Index>) -> String {
    // TODO: Make unreachable when the Foundation overlay is off of Swift 3
    _boundsCheck(bounds)
    return String(Substring(_slice: Slice(base: self, bounds: bounds)))
  }

  @available(swift, obsoleted: 4)
  public subscript(bounds: ClosedRange<Index>) -> String {
    // TODO: Make unreachable when the Foundation overlay is off of Swift 3
    let r = bounds.relative(to: self)
    _boundsCheck(r)
    return String(Substring(_slice: Slice(
          base: self,
          bounds: r)))
  }
}

//===--- Slicing Support --------------------------------------------------===//
// In Swift 3.2, in the absence of type context,
//
//   someString.unicodeScalars[
//     someString.unicodeScalars.startIndex
//     ..< someString.unicodeScalars.endIndex]
//
// was deduced to be of type `String.UnicodeScalarView`.  Provide a
// more-specific Swift-3-only `subscript` overload that continues to produce
// `String.UnicodeScalarView`.
extension String.UnicodeScalarView {
  @available(swift, obsoleted: 4)
  public subscript(bounds: Range<Index>) -> String.UnicodeScalarView {
    Builtin.unreachable()
  }

  @available(swift, obsoleted: 4)
  public subscript(bounds: ClosedRange<Index>) -> String.UnicodeScalarView {
    Builtin.unreachable()
  }
}

//===--- Slicing Support --------------------------------------------------===//
// In Swift 3.2, in the absence of type context,
//
//   someString.utf16[someString.utf16.startIndex..<someString.utf16.endIndex]
//
// was deduced to be of type `String.UTF16View`.  Provide a more-specific
// Swift-3-only `subscript` overload that continues to produce
// `String.UTF16View`.
extension String.UTF16View {
  @available(swift, obsoleted: 4)
  public subscript(bounds: Range<Index>) -> String.UTF16View {
    Builtin.unreachable()
  }

  @available(swift, obsoleted: 4)
  public subscript(bounds: ClosedRange<Index>) -> String.UTF16View {
    Builtin.unreachable()
  }
}

//===--- Slicing Support --------------------------------------------------===//
/// In Swift 3.2, in the absence of type context,
///
///   someString.utf8[someString.utf8.startIndex..<someString.utf8.endIndex]
///
/// was deduced to be of type `String.UTF8View`.  Provide a more-specific
/// Swift-3-only `subscript` overload that continues to produce
/// `String.UTF8View`.
extension String.UTF8View {
  @available(swift, obsoleted: 4)
  public subscript(bounds: Range<Index>) -> String.UTF8View {
    Builtin.unreachable()
  }


  @available(swift, obsoleted: 4)
  public subscript(bounds: ClosedRange<Index>) -> String.UTF8View {
    Builtin.unreachable()
  }
}

// @available(swift,deprecated: 5.0, renamed: "Unicode.UTF8")
public typealias UTF8 = Unicode.UTF8
// @available(swift, deprecated: 5.0, renamed: "Unicode.UTF16")
public typealias UTF16 = Unicode.UTF16
// @available(swift, deprecated: 5.0, renamed: "Unicode.UTF32")
public typealias UTF32 = Unicode.UTF32
// @available(swift, deprecated: 5.0, renamed: "Unicode.Scalar")
public typealias UnicodeScalar = Unicode.Scalar


// popFirst() is only present when a collection is its own subsequence. This was
// dropped in Swift 4.
extension String {
  @available(swift, deprecated: 3.2, obsoleted: 4, message: "Please use 'first', 'dropFirst()', or 'Substring.popFirst()'.")
  public mutating func popFirst() -> String.Element? {
    Builtin.unreachable()
  }
}

extension String.UnicodeScalarView {
  @available(swift, deprecated: 3.2, obsoleted: 4, message: "Please use 'first', 'dropFirst()', or 'Substring.UnicodeScalarView.popFirst()'.")
  public mutating func popFirst() -> String.UnicodeScalarView.Element? {
    Builtin.unreachable()
  }
}

extension String.UTF16View : _CustomPlaygroundQuickLookable {
  @available(swift, deprecated: 4.2/*, obsoleted: 5.0*/, message: "UTF16View.customPlaygroundQuickLook will be removed in Swift 5.0")
  public var customPlaygroundQuickLook: _PlaygroundQuickLook {
    return .text(description)
  }
}

extension String.UTF8View : _CustomPlaygroundQuickLookable {
  @available(swift, deprecated: 4.2/*, obsoleted: 5.0*/, message: "UTF8View.customPlaygroundQuickLook will be removed in Swift 5.0")
  public var customPlaygroundQuickLook: _PlaygroundQuickLook {
    return .text(description)
  }
}

extension StringProtocol {
  @available(swift, deprecated: 3.2, obsoleted: 4.0, renamed: "UTF8View.Index")
  public typealias UTF8Index = UTF8View.Index
  @available(swift, deprecated: 3.2, obsoleted: 4.0, renamed: "UTF16View.Index")
  public typealias UTF16Index = UTF16View.Index
  @available(swift, deprecated: 3.2, obsoleted: 4.0, renamed: "UnicodeScalarView.Index")
  public typealias UnicodeScalarIndex = UnicodeScalarView.Index
}

extension Substring {
  /// A view of a string's contents as a collection of characters.
  ///
  /// Previous versions of Swift provided this view since String
  /// itself was not a collection. String is now a collection of
  /// characters, so this type is now just an alias for String.
  @available(swift, deprecated: 3.2, obsoleted: 5.0, message: "Please use Substring directly")
  public typealias CharacterView = Substring

  /// A view of the string's contents as a collection of characters.
  @available(swift, deprecated: 3.2, obsoleted: 5.0, message: "Please use Substring directly")
  public var characters: Substring {
    get {
      return self
    }
    set {
      self = newValue
    }
  }

  /// Applies the given closure to a mutable view of the string's characters.
  ///
  /// Previous versions of Swift provided this view since String
  /// itself was not a collection. String is now a collection of
  /// characters, so this type is now just an alias for String.
  @available(swift, deprecated: 3.2, obsoleted: 5.0, message: "Please mutate the Substring directly")
  public mutating func withMutableCharacters<R>(
    _ body: (inout Substring) -> R
  ) -> R {
    return body(&self)
  }

  private func _boundsCheck(_ range: Range<Index>) {
    _precondition(range.lowerBound >= startIndex,
      "String index range is out of bounds")
    _precondition(range.upperBound <= endIndex,
      "String index range is out of bounds")
  }

  @available(swift, obsoleted: 4)
  public subscript(bounds: ClosedRange<Index>) -> String {
    Builtin.unreachable()
  }
}

extension Substring : _CustomPlaygroundQuickLookable {
  @available(swift, deprecated: 4.2/*, obsoleted: 5.0*/, message: "Substring.customPlaygroundQuickLook will be removed in Swift 5.0")
  public var customPlaygroundQuickLook: _PlaygroundQuickLook {
    return String(self).customPlaygroundQuickLook
  }
}

extension Collection {
  // FIXME: <rdar://problem/34142121>
  // This typealias should be removed as it predates the source compatibility
  // guarantees of Swift 3, but it cannot due to a bug.
  @available(*, unavailable, renamed: "Iterator")
  public typealias Generator = Iterator

  @available(swift, deprecated: 3.2, obsoleted: 5.0, renamed: "Element")
  public typealias _Element = Element

  @available(swift, deprecated: 4.0, obsoleted: 5.0, message: "all index distances are now of type Int")
  public func index<T: BinaryInteger>(_ i: Index, offsetBy n: T) -> Index {
    return index(i, offsetBy: Int(n))
  }
  @available(swift, deprecated: 4.0, obsoleted: 5.0, message: "all index distances are now of type Int")
  public func formIndex<T: BinaryInteger>(_ i: inout Index, offsetBy n: T) {
    return formIndex(&i, offsetBy: Int(n))
  }
  @available(swift, deprecated: 4.0, obsoleted: 5.0, message: "all index distances are now of type Int")
  public func index<T: BinaryInteger>(_ i: Index, offsetBy n: T, limitedBy limit: Index) -> Index? {
    return index(i, offsetBy: Int(n), limitedBy: limit)
  }
  @available(swift, deprecated: 4.0, obsoleted: 5.0, message: "all index distances are now of type Int")
  public func formIndex<T: BinaryInteger>(_ i: inout Index, offsetBy n: T, limitedBy limit: Index) -> Bool {
    return formIndex(&i, offsetBy: Int(n), limitedBy: limit)
  }
  @available(swift, deprecated: 4.0, obsoleted: 5.0, message: "all index distances are now of type Int")
  public func distance<T: BinaryInteger>(from start: Index, to end: Index) -> T {
    return numericCast(distance(from: start, to: end) as Int)
  }
}


extension UnsafeMutablePointer {
  @available(swift, deprecated: 4.1, obsoleted: 5.0, renamed: "initialize(repeating:count:)")
  public func initialize(to newValue: Pointee, count: Int = 1) { 
    initialize(repeating: newValue, count: count)
  }

  @available(swift, deprecated: 4.1, obsoleted: 5.0, message: "the default argument to deinitialize(count:) has been removed, please specify the count explicitly") 
  @discardableResult
  public func deinitialize() -> UnsafeMutableRawPointer {
    return deinitialize(count: 1)
  }
  
  @available(swift, deprecated: 4.1, obsoleted: 5.0, message: "Swift currently only supports freeing entire heap blocks, use deallocate() instead")
  public func deallocate(capacity _: Int) { 
    self.deallocate()
  }

  /// Initializes memory starting at this pointer's address with the elements
  /// of the given collection.
  ///
  /// The region of memory starting at this pointer and covering `source.count`
  /// instances of the pointer's `Pointee` type must be uninitialized or
  /// `Pointee` must be a trivial type. After calling `initialize(from:)`, the
  /// region is initialized.
  ///
  /// - Parameter source: A collection of elements of the pointer's `Pointee`
  ///   type.
  // This is fundamentally unsafe since collections can underreport their count.
  @available(swift, deprecated: 4.2, obsoleted: 5.0, message: "it will be removed in Swift 5.0.  Please use 'UnsafeMutableBufferPointer.initialize(from:)' instead")
  public func initialize<C : Collection>(from source: C)
    where C.Element == Pointee {
    let buf = UnsafeMutableBufferPointer(start: self, count: numericCast(source.count))
    var (remainders,writtenUpTo) = source._copyContents(initializing: buf)
    // ensure that exactly rhs.count elements were written
    _precondition(remainders.next() == nil, "rhs underreported its count")
    _precondition(writtenUpTo == buf.endIndex, "rhs overreported its count")
  }
}

extension Strideable {
  @available(swift, deprecated: 3, obsoleted: 4, message: "Please use explicit type conversions or Strideable methods for mixed-type arithmetics.")
  public static func + (lhs: Self, rhs: Self.Stride) -> Self {
    return lhs.advanced(by: rhs)
  }

  @available(swift, deprecated: 3, obsoleted: 4, message: "Please use explicit type conversions or Strideable methods for mixed-type arithmetics.")
  public static func + (lhs: Self.Stride, rhs: Self) -> Self {
    return rhs.advanced(by: lhs)
  }

  @available(swift, deprecated: 3, obsoleted: 4, message: "Please use explicit type conversions or Strideable methods for mixed-type arithmetics.")
  public static func - (lhs: Self, rhs: Self.Stride) -> Self {
    return lhs.advanced(by: -rhs)
  }

  @available(swift, deprecated: 3, obsoleted: 4, message: "Please use explicit type conversions or Strideable methods for mixed-type arithmetics.")
  public static func - (lhs: Self, rhs: Self) -> Self.Stride {
    return rhs.distance(to: lhs)
  }

  @available(swift, deprecated: 3, obsoleted: 4, message: "Please use explicit type conversions or Strideable methods for mixed-type arithmetics.")
  public static func += (lhs: inout Self, rhs: Self.Stride) {
    lhs = lhs.advanced(by: rhs)
  }

  @available(swift, deprecated: 3, obsoleted: 4, message: "Please use explicit type conversions or Strideable methods for mixed-type arithmetics.")
  public static func -= (lhs: inout Self, rhs: Self.Stride) {
    lhs = lhs.advanced(by: -rhs)
  }
}

extension UnsafeMutableRawPointer {
  @available(*, unavailable, renamed: "init(mutating:)")
  public init(_ from : UnsafeRawPointer) { Builtin.unreachable() }

  @available(*, unavailable, renamed: "init(mutating:)")
  public init?(_ from : UnsafeRawPointer?) { Builtin.unreachable() }

  @available(*, unavailable, renamed: "init(mutating:)")
  public init<T>(_ from : UnsafePointer<T>) { Builtin.unreachable() }

  @available(*, unavailable, renamed: "init(mutating:)")
  public init?<T>(_ from : UnsafePointer<T>?) { Builtin.unreachable() }
}

extension UnsafeRawPointer : _CustomPlaygroundQuickLookable {
  internal var summary: String {
    let ptrValue = UInt64(
      bitPattern: Int64(Int(Builtin.ptrtoint_Word(_rawValue))))
    return ptrValue == 0
    ? "UnsafeRawPointer(nil)"
    : "UnsafeRawPointer(0x\(_uint64ToString(ptrValue, radix:16, uppercase:true)))"
  }

  @available(swift, deprecated: 4.2/*, obsoleted: 5.0*/, message: "UnsafeRawPointer.customPlaygroundQuickLook will be removed in a future Swift version")
  public var customPlaygroundQuickLook: _PlaygroundQuickLook {
    return .text(summary)
  }
}

extension UnsafeMutableRawPointer : _CustomPlaygroundQuickLookable {
  private var summary: String {
    let ptrValue = UInt64(
      bitPattern: Int64(Int(Builtin.ptrtoint_Word(_rawValue))))
    return ptrValue == 0
    ? "UnsafeMutableRawPointer(nil)"
    : "UnsafeMutableRawPointer(0x\(_uint64ToString(ptrValue, radix:16, uppercase:true)))"
  }

  @available(swift, deprecated: 4.2/*, obsoleted: 5.0*/, message: "UnsafeMutableRawPointer.customPlaygroundQuickLook will be removed in a future Swift version")
  public var customPlaygroundQuickLook: _PlaygroundQuickLook {
    return .text(summary)
  }
}

extension UnsafePointer: _CustomPlaygroundQuickLookable {
  private var summary: String {
    let ptrValue = UInt64(bitPattern: Int64(Int(Builtin.ptrtoint_Word(_rawValue))))
    return ptrValue == 0 
    ? "UnsafePointer(nil)" 
    : "UnsafePointer(0x\(_uint64ToString(ptrValue, radix:16, uppercase:true)))"
  }

  @available(swift, deprecated: 4.2/*, obsoleted: 5.0*/, message: "UnsafePointer.customPlaygroundQuickLook will be removed in a future Swift version")
  public var customPlaygroundQuickLook: PlaygroundQuickLook {
    return .text(summary)
  }
}

extension UnsafeMutablePointer: _CustomPlaygroundQuickLookable {
  private var summary: String {
    let ptrValue = UInt64(bitPattern: Int64(Int(Builtin.ptrtoint_Word(_rawValue))))
    return ptrValue == 0 
    ? "UnsafeMutablePointer(nil)" 
    : "UnsafeMutablePointer(0x\(_uint64ToString(ptrValue, radix:16, uppercase:true)))"
  }

  @available(swift, deprecated: 4.2/*, obsoleted: 5.0*/, message: "UnsafeMutablePointer.customPlaygroundQuickLook will be removed in a future Swift version")
  public var customPlaygroundQuickLook: PlaygroundQuickLook {
    return .text(summary)
  }
}

@available(swift, deprecated: 4.1, obsoleted: 5.0, renamed: "UnsafeBufferPointer.Iterator")
public typealias UnsafeBufferPointerIterator<T> = UnsafeBufferPointer<T>.Iterator
@available(swift, deprecated: 4.1, obsoleted: 5.0, renamed: "UnsafeRawBufferPointer.Iterator")
public typealias UnsafeRawBufferPointerIterator<T> = UnsafeBufferPointer<T>.Iterator
@available(swift, deprecated: 4.1, obsoleted: 5.0, renamed: "UnsafeRawBufferPointer.Iterator")
public typealias UnsafeMutableRawBufferPointerIterator<T> = UnsafeBufferPointer<T>.Iterator

extension UnsafeMutableRawPointer {
  @available(swift, deprecated: 4.1, obsoleted: 5.0, renamed: "allocate(byteCount:alignment:)")
  public static func allocate(
    bytes size: Int, alignedTo alignment: Int
  ) -> UnsafeMutableRawPointer {
    return UnsafeMutableRawPointer.allocate(byteCount: size, alignment: alignment)
  }
  
  @available(swift, deprecated: 4.1, obsoleted: 5.0, renamed: "deallocate()", message: "Swift currently only supports freeing entire heap blocks, use deallocate() instead")
  public func deallocate(bytes _: Int, alignedTo _: Int) { 
    self.deallocate()
  }

  @available(swift, deprecated: 4.1, obsoleted: 5.0, renamed: "copyMemory(from:byteCount:)")
  public func copyBytes(from source: UnsafeRawPointer, count: Int) {
    copyMemory(from: source, byteCount: count)
  }

  @available(swift, deprecated: 4.1, obsoleted: 5.0, renamed: "initializeMemory(as:repeating:count:)")
  @discardableResult
  public func initializeMemory<T>(
    as type: T.Type, at offset: Int = 0, count: Int = 1, to repeatedValue: T
  ) -> UnsafeMutablePointer<T> { 
    return (self + offset * MemoryLayout<T>.stride).initializeMemory(
      as: type, repeating: repeatedValue, count: count)
  }

  @available(swift, deprecated: 4.1, obsoleted: 5.0, message: "it will be removed in Swift 5.0.  Please use 'UnsafeMutableRawBufferPointer.initialize(from:)' instead")
  @discardableResult
  public func initializeMemory<C : Collection>(
    as type: C.Element.Type, from source: C
  ) -> UnsafeMutablePointer<C.Element> {
    // TODO: Optimize where `C` is a `ContiguousArrayBuffer`.
    // Initialize and bind each element of the container.
    var ptr = self
    for element in source {
      ptr.initializeMemory(as: C.Element.self, repeating: element, count: 1)
      ptr += MemoryLayout<C.Element>.stride
    }
    return UnsafeMutablePointer(_rawValue)
  }
}

extension UnsafeMutableRawBufferPointer {
  @available(swift, deprecated: 4.1, obsoleted: 5.0, renamed: "allocate(byteCount:alignment:)")
  public static func allocate(count: Int) -> UnsafeMutableRawBufferPointer { 
    return UnsafeMutableRawBufferPointer.allocate(
      byteCount: count, alignment: MemoryLayout<UInt>.alignment)
  }

  @available(swift, deprecated: 4.1, obsoleted: 5.0, renamed: "copyMemory(from:)")
  public func copyBytes(from source: UnsafeRawBufferPointer) {
    copyMemory(from: source)
  }
}

//===----------------------------------------------------------------------===//
// The following overloads of flatMap are carefully crafted to allow the code
// like the following:
//   ["hello"].flatMap { $0 }
// return an array of strings without any type context in Swift 3 mode, at the
// same time allowing the following code snippet to compile:
//   [0, 1].flatMap { x in
//     if String(x) == "foo" { return "bar" } else { return nil }
//   }
// Note that the second overload is declared on a more specific protocol.
// See: test/stdlib/StringFlatMap.swift for tests.
extension Sequence {
  @available(swift, deprecated: 4.1/*, obsoleted: 5.0*/, renamed: "compactMap(_:)",
    message: "Please use compactMap(_:) for the case where closure returns an optional value")
  public func flatMap<ElementOfResult>(
    _ transform: (Element) throws -> ElementOfResult?
  ) rethrows -> [ElementOfResult] {
    return try _compactMap(transform)
  }

  @available(swift, obsoleted: 4)
  public func flatMap(
    _ transform: (Element) throws -> String
  ) rethrows -> [String] {
    return try map(transform)
  }
}

extension Collection {
  @available(swift, deprecated: 4.1, obsoleted: 5.0, renamed: "compactMap(_:)", message: "Please use compactMap(_:) for the case where closure returns an optional value")
  public func flatMap(
    _ transform: (Element) throws -> String?
  ) rethrows -> [String] {
    return try _compactMap(transform)
  }
}

extension Collection {
  /// Returns the first index in which an element of the collection satisfies
  /// the given predicate.
  @available(swift, deprecated: 5.0, renamed: "firstIndex(where:)")
  @inlinable
  public func index(
    where _predicate: (Element) throws -> Bool
  ) rethrows -> Index? {
    return try firstIndex(where: _predicate)
  }
}

extension Collection where Element: Equatable {
  /// Returns the first index where the specified value appears in the
  /// collection.
  @available(swift, deprecated: 5.0, renamed: "firstIndex(of:)")
  @inlinable
  public func index(of element: Element) -> Index? {
    return firstIndex(of: element)
  }
}

extension String.Index {
  @available(swift, deprecated: 3.2, obsoleted: 4.0)
  public init(_position: Int) {
    self.init(encodedOffset: _position)
  }

  @available(swift, deprecated: 3.2, obsoleted: 4.0)
  public init(_codeUnitOffset: Int) {
    self.init(encodedOffset: _codeUnitOffset)
  }

  @available(swift, deprecated: 3.2, obsoleted: 4.0)
  public var _utf16Index: Int {
    return self.encodedOffset
  }

  @available(swift, deprecated: 3.2, obsoleted: 4.0)
  public var _offset: Int {
    return self.encodedOffset
  }
}

// backward compatibility for index interchange.
extension Optional where Wrapped == String.Index {
  @available(swift, obsoleted: 4.0, message: "Any String view index conversion can fail in Swift 4; please unwrap the optional indices")
  public static func ..<(
    lhs: String.Index?, rhs: String.Index?
  ) -> Range<String.Index> {
    return lhs! ..< rhs!
  }

  @available(swift, obsoleted: 4.0, message: "Any String view index conversion can fail in Swift 4; please unwrap the optional indices")
  public static func ...(
    lhs: String.Index?, rhs: String.Index?
  ) -> ClosedRange<String.Index> {
    return lhs! ... rhs!
  }
}

extension Zip2Sequence {
  @available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "Sequence1.Iterator")
  public typealias Stream1 = Sequence1.Iterator
  @available(swift, deprecated: 4.2, obsoleted: 5.0, renamed: "Sequence2.Iterator")
  public typealias Stream2 = Sequence2.Iterator
}


//===--- QuickLooks -------------------------------------------------------===//

/// The sum of types that can be used as a Quick Look representation.
///
/// The `PlaygroundQuickLook` protocol is deprecated, and will be removed from
/// the standard library in a future Swift release. To customize the logging of
/// your type in a playground, conform to the
/// `CustomPlaygroundDisplayConvertible` protocol, which does not use the
/// `PlaygroundQuickLook` enum.
///
/// If you need to provide a customized playground representation in Swift 4.0
/// or Swift 3.2 or earlier, use a conditional compilation block:
///
///     #if swift(>=4.1) || (swift(>=3.3) && !swift(>=4.0))
///         // With Swift 4.1 and later (including Swift 3.3 and later), use
///         // the CustomPlaygroundDisplayConvertible protocol.
///     #else
///         // With Swift 4.0 and Swift 3.2 and earlier, use PlaygroundQuickLook
///         // and the CustomPlaygroundQuickLookable protocol.
///     #endif
@available(swift, deprecated: 4.2, message: "PlaygroundQuickLook will be removed in a future Swift version. For customizing how types are presented in playgrounds, use CustomPlaygroundDisplayConvertible instead.")
public typealias PlaygroundQuickLook = _PlaygroundQuickLook

@_frozen // rdar://problem/38719739 - needed by LLDB
public enum _PlaygroundQuickLook {
  case text(String)
  case int(Int64)
  case uInt(UInt64)
  case float(Float32)
  case double(Float64)
  case image(Any)
  case sound(Any)
  case color(Any)
  case bezierPath(Any)
  case attributedString(Any)
  case rectangle(Float64, Float64, Float64, Float64)
  case point(Float64, Float64)
  case size(Float64, Float64)
  case bool(Bool)
  case range(Int64, Int64)
  case view(Any)
  case sprite(Any)
  case url(String)
  case _raw([UInt8], String)
}

// Maintain old `keys` and `values` types in Swift 3 mode.
extension Dictionary {
  /// A collection containing just the keys of the dictionary.
  ///
  /// When iterated over, keys appear in this collection in the same order as
  /// they occur in the dictionary's key-value pairs. Each key in the keys
  /// collection has a unique value.
  ///
  ///     let countryCodes = ["BR": "Brazil", "GH": "Ghana", "JP": "Japan"]
  ///     print(countryCodes)
  ///     // Prints "["BR": "Brazil", "JP": "Japan", "GH": "Ghana"]"
  ///
  ///     for k in countryCodes.keys {
  ///         print(k)
  ///     }
  ///     // Prints "BR"
  ///     // Prints "JP"
  ///     // Prints "GH"
  @available(swift, obsoleted: 4.0)
  public var keys: LazyMapCollection<[Key: Value], Key> {
    return self.lazy.map { $0.key }
  }

  /// A collection containing just the values of the dictionary.
  ///
  /// When iterated over, values appear in this collection in the same order as
  /// they occur in the dictionary's key-value pairs.
  ///
  ///     let countryCodes = ["BR": "Brazil", "GH": "Ghana", "JP": "Japan"]
  ///     print(countryCodes)
  ///     // Prints "["BR": "Brazil", "JP": "Japan", "GH": "Ghana"]"
  ///
  ///     for v in countryCodes.values {
  ///         print(v)
  ///     }
  ///     // Prints "Brazil"
  ///     // Prints "Japan"
  ///     // Prints "Ghana"
  @available(swift, obsoleted: 4.0)
  public var values: LazyMapCollection<[Key: Value], Value> {
    return self.lazy.map { $0.value }
  }

  @available(swift, obsoleted: 4.0)
  public func filter(
    _ isIncluded: (Element) throws -> Bool, obsoletedInSwift4: () = ()
  ) rethrows -> [Element] {
    var result: [Element] = []
    for x in self {
      if try isIncluded(x) {
        result.append(x)
      }
    }
    return result
  }
}

extension Set {
  @available(swift, obsoleted: 4.0)
  public func filter(
    _ isIncluded: (Element) throws -> Bool, obsoletedInSwift4: () = ()
  ) rethrows -> [Element] {
    var result: [Element] = []
    for x in self {
      if try isIncluded(x) {
        result.append(x)
      }
    }
    return result
  }  
}

extension _PlaygroundQuickLook {
  /// Creates a new Quick Look for the given instance.
  ///
  /// If the dynamic type of `subject` conforms to
  /// `CustomPlaygroundQuickLookable`, the result is found by calling its
  /// `customPlaygroundQuickLook` property. Otherwise, the result is
  /// synthesized by the language. In some cases, the synthesized result may
  /// be `.text(String(reflecting: subject))`.
  ///
  /// - Note: If the dynamic type of `subject` has value semantics, subsequent
  ///   mutations of `subject` will not observable in the Quick Look. In
  ///   general, though, the observability of such mutations is unspecified.
  ///
  /// - Parameter subject: The instance to represent with the resulting Quick
  ///   Look.
  @available(swift, deprecated: 4.2, obsoleted: 5.0, message: "PlaygroundQuickLook will be removed in a future Swift version.")
  public init(reflecting subject: Any) {
    if let customized = subject as? _CustomPlaygroundQuickLookable {
      self = customized.customPlaygroundQuickLook
    }
    else if let customized = subject as? __DefaultCustomPlaygroundQuickLookable {
      self = customized._defaultCustomPlaygroundQuickLook
    }
    else {
      if let q = Mirror.quickLookObject(subject) {
        self = q
      }
      else {
        self = .text(String(reflecting: subject))
      }
    }
  }
}

/// A type that explicitly supplies its own playground Quick Look.
///
/// The `CustomPlaygroundQuickLookable` protocol is deprecated, and will be
/// removed from the standard library in a future Swift release. To customize
/// the logging of your type in a playground, conform to the
/// `CustomPlaygroundDisplayConvertible` protocol.
///
/// If you need to provide a customized playground representation in Swift 4.0
/// or Swift 3.2 or earlier, use a conditional compilation block:
///
///     #if swift(>=4.1) || (swift(>=3.3) && !swift(>=4.0))
///         // With Swift 4.1 and later (including Swift 3.3 and later),
///         // conform to CustomPlaygroundDisplayConvertible.
///         extension MyType: CustomPlaygroundDisplayConvertible { /*...*/ }
///     #else
///         // Otherwise, on Swift 4.0 and Swift 3.2 and earlier,
///         // conform to CustomPlaygroundQuickLookable.
///         extension MyType: CustomPlaygroundQuickLookable { /*...*/ }
///     #endif
@available(swift, deprecated: 4.2, obsoleted: 5.0, message: "CustomPlaygroundQuickLookable will be removed in a future Swift version. For customizing how types are presented in playgrounds, use CustomPlaygroundDisplayConvertible instead.")
public typealias CustomPlaygroundQuickLookable = _CustomPlaygroundQuickLookable

//@available(swift, obsoleted: 5.0)
public protocol _CustomPlaygroundQuickLookable {
  /// A custom playground Quick Look for this instance.
  ///
  /// If this type has value semantics, the `PlaygroundQuickLook` instance
  /// should be unaffected by subsequent mutations.
  var customPlaygroundQuickLook: _PlaygroundQuickLook { get }
}

// Double-underscored real version allows us to keep using this in AppKit while
// warning for non-SDK use. This is probably overkill but it doesn't cost
// anything.
@available(swift, deprecated: 4.2, obsoleted: 5.0, message: "_DefaultCustomPlaygroundQuickLookable will be removed in a future Swift version. For customizing how types are presented in playgrounds, use CustomPlaygroundDisplayConvertible instead.")
public typealias _DefaultCustomPlaygroundQuickLookable = __DefaultCustomPlaygroundQuickLookable

// @available(swift, obsoleted: 5.0)
public protocol __DefaultCustomPlaygroundQuickLookable {
  var _defaultCustomPlaygroundQuickLook: _PlaygroundQuickLook { get }
}