stdlib/public/core/StringUnicodeScalarView.swift - third_party/swift - Git at Google

 //===----------------------------------------------------------------------===//
 //
 // This source file is part of the Swift.org open source project
 //
 // Copyright (c) 2014 - 2017 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
 //
 //===----------------------------------------------------------------------===//

 extension String {
   /// A view of a string's contents as a collection of Unicode scalar values.
   ///
   /// You can access a string's view of Unicode scalar values by using its
   /// `unicodeScalars` property. Unicode scalar values are the 21-bit codes
   /// that are the basic unit of Unicode. Each scalar value is represented by
   /// a `Unicode.Scalar` instance and is equivalent to a UTF-32 code unit.
   ///
   ///     let flowers = "Flowers 💐"
   ///     for v in flowers.unicodeScalars {
   ///         print(v.value)
   ///     }
   ///     // 70
   ///     // 108
   ///     // 111
   ///     // 119
   ///     // 101
   ///     // 114
   ///     // 115
   ///     // 32
   ///     // 128144
   ///
   /// Some characters that are visible in a string are made up of more than one
   /// Unicode scalar value. In that case, a string's `unicodeScalars` view
   /// contains more elements than the string itself.
   ///
   ///     let flag = "🇵🇷"
   ///     for c in flag {
   ///         print(c)
   ///     }
   ///     // 🇵🇷
   ///
   ///     for v in flag.unicodeScalars {
   ///         print(v.value)
   ///     }
   ///     // 127477
   ///     // 127479
   ///
   /// You can convert a `String.UnicodeScalarView` instance back into a string
   /// using the `String` type's `init(_:)` initializer.
   ///
   ///     let favemoji = "My favorite emoji is 🎉"
   ///     if let i = favemoji.unicodeScalars.index(where: { $0.value >= 128 }) {
   ///         let asciiPrefix = String(favemoji.unicodeScalars[..<i])
   ///         print(asciiPrefix)
   ///     }
   ///     // Prints "My favorite emoji is "
   @_fixed_layout // FIXME(sil-serialize-all)
   public struct UnicodeScalarView :
     BidirectionalCollection,
     CustomStringConvertible,
     CustomDebugStringConvertible
   {
     @_inlineable // FIXME(sil-serialize-all)
     @_versioned // FIXME(sil-serialize-all)
     internal init(_ _core: _StringCore, coreOffset: Int = 0) {
       self._core = _core
       self._coreOffset = coreOffset
     }

     @_fixed_layout // FIXME(sil-serialize-all)
     @_versioned // FIXME(sil-serialize-all)
     internal struct _ScratchIterator : IteratorProtocol {
       @_versioned
       internal var core: _StringCore
       @_versioned // FIXME(sil-serialize-all)
       internal var idx: Int
       @_inlineable // FIXME(sil-serialize-all)
       @_versioned // FIXME(sil-serialize-all)
       internal init(_ core: _StringCore, _ pos: Int) {
         self.idx = pos
         self.core = core
       }
       @_inlineable // FIXME(sil-serialize-all)
       @_versioned // FIXME(sil-serialize-all)
       @inline(__always)
       internal mutating func next() -> UTF16.CodeUnit? {
         if idx == core.endIndex {
           return nil
         }
         defer { idx += 1 }
         return self.core[idx]
       }
     }

     public typealias Index = String.Index

     /// Translates a `_core` index into a `UnicodeScalarIndex` using this view's
     /// `_coreOffset`.
     @_inlineable // FIXME(sil-serialize-all)
     @_versioned // FIXME(sil-serialize-all)
     internal func _fromCoreIndex(_ i: Int) -> Index {
       return Index(encodedOffset: i + _coreOffset)
     }

     /// Translates a `UnicodeScalarIndex` into a `_core` index using this view's
     /// `_coreOffset`.
     @_inlineable // FIXME(sil-serialize-all)
     @_versioned // FIXME(sil-serialize-all)
     internal func _toCoreIndex(_ i: Index) -> Int {
       return i.encodedOffset - _coreOffset
     }

     /// The position of the first Unicode scalar value if the string is
     /// nonempty.
     ///
     /// If the string is empty, `startIndex` is equal to `endIndex`.
     @_inlineable // FIXME(sil-serialize-all)
     public var startIndex: Index {
       return _fromCoreIndex(_core.startIndex)
     }

     /// The "past the end" position---that is, the position one greater than
     /// the last valid subscript argument.
     ///
     /// In an empty Unicode scalars view, `endIndex` is equal to `startIndex`.
     @_inlineable // FIXME(sil-serialize-all)
     public var endIndex: Index {
       return _fromCoreIndex(_core.endIndex)
     }

     /// Returns the next consecutive location after `i`.
     ///
     /// - Precondition: The next location exists.
     @_inlineable // FIXME(sil-serialize-all)
     public func index(after i: Index) -> Index {
       let i = _toCoreIndex(i)
       var scratch = _ScratchIterator(_core, i)
       var decoder = UTF16()
       let (_, length) = decoder._decodeOne(&scratch)
       return _fromCoreIndex(i + length)
     }

     /// Returns the previous consecutive location before `i`.
     ///
     /// - Precondition: The previous location exists.
     @_inlineable // FIXME(sil-serialize-all)
     public func index(before i: Index) -> Index {
       var i = _toCoreIndex(i) - 1
       let codeUnit = _core[i]
       if _slowPath((codeUnit >> 10) == 0b1101_11) {
         if i != 0 && (_core[i - 1] >> 10) == 0b1101_10 {
           i -= 1
         }
       }
       return _fromCoreIndex(i)
     }

     /// Accesses the Unicode scalar value at the given position.
     ///
     /// The following example searches a string's Unicode scalars view for a
     /// capital letter and then prints the character and Unicode scalar value
     /// at the found index:
     ///
     ///     let greeting = "Hello, friend!"
     ///     if let i = greeting.unicodeScalars.index(where: { "A"..."Z" ~= $0 }) {
     ///         print("First capital letter: \(greeting.unicodeScalars[i])")
     ///         print("Unicode scalar value: \(greeting.unicodeScalars[i].value)")
     ///     }
     ///     // Prints "First capital letter: H"
     ///     // Prints "Unicode scalar value: 72"
     ///
     /// - Parameter position: A valid index of the character view. `position`
     ///   must be less than the view's end index.
     @_inlineable // FIXME(sil-serialize-all)
     public subscript(position: Index) -> Unicode.Scalar {
       var scratch = _ScratchIterator(_core, _toCoreIndex(position))
       var decoder = UTF16()
       switch decoder.decode(&scratch) {
       case .scalarValue(let us):
         return us
       case .emptyInput:
         _sanityCheckFailure("cannot subscript using an endIndex")
       case .error:
         return Unicode.Scalar(0xfffd)!
       }
     }

     /// An iterator over the Unicode scalars that make up a `UnicodeScalarView`
     /// collection.
     @_fixed_layout // FIXME(sil-serialize-all)
     public struct Iterator : IteratorProtocol {
       @_inlineable // FIXME(sil-serialize-all)
       @_versioned // FIXME(sil-serialize-all)
       internal init(_ _base: _StringCore) {
         self._iterator = _base.makeIterator()
         if _base.hasContiguousStorage {
           self._baseSet = true
           if _base.isASCII {
             self._ascii = true
             self._asciiBase = UnsafeBufferPointer(
               start: _base._baseAddress?.assumingMemoryBound(
                 to: UTF8.CodeUnit.self),
               count: _base.count).makeIterator()
           } else {
             self._ascii = false
             self._base = UnsafeBufferPointer<UInt16>(
               start: _base._baseAddress?.assumingMemoryBound(
                 to: UTF16.CodeUnit.self),
               count: _base.count).makeIterator()
           }
         } else {
           self._ascii = false
           self._baseSet = false
         }
       }

       /// Advances to the next element and returns it, or `nil` if no next
       /// element exists.
       ///
       /// Once `nil` has been returned, all subsequent calls return `nil`.
       ///
       /// - Precondition: `next()` has not been applied to a copy of `self`
       ///   since the copy was made.
       @_inlineable // FIXME(sil-serialize-all)
       public mutating func next() -> Unicode.Scalar? {
         var result: UnicodeDecodingResult
         if _baseSet {
           if _ascii {
             switch self._asciiBase.next() {
             case let x?:
               result = .scalarValue(Unicode.Scalar(x))
             case nil:
               result = .emptyInput
             }
           } else {
             result = _decoder.decode(&(self._base!))
           }
         } else {
           result = _decoder.decode(&(self._iterator))
         }
         switch result {
         case .scalarValue(let us):
           return us
         case .emptyInput:
           return nil
         case .error:
           return Unicode.Scalar(0xfffd)
         }
       }
       @_versioned // FIXME(sil-serialize-all)
       internal var _decoder: UTF16 = UTF16()
       @_versioned // FIXME(sil-serialize-all)
       internal let _baseSet: Bool
       @_versioned // FIXME(sil-serialize-all)
       internal let _ascii: Bool
       @_versioned // FIXME(sil-serialize-all)
       internal var _asciiBase: UnsafeBufferPointerIterator<UInt8>!
       @_versioned // FIXME(sil-serialize-all)
       internal var _base: UnsafeBufferPointerIterator<UInt16>!
       @_versioned // FIXME(sil-serialize-all)
       internal var _iterator: IndexingIterator<_StringCore>
     }

     /// Returns an iterator over the Unicode scalars that make up this view.
     ///
     /// - Returns: An iterator over this collection's `Unicode.Scalar` elements.
     @_inlineable // FIXME(sil-serialize-all)
     public func makeIterator() -> Iterator {
       return Iterator(_core)
     }

     @_inlineable // FIXME(sil-serialize-all)
     public var description: String {
       return String(_core)
     }

     @_inlineable // FIXME(sil-serialize-all)
     public var debugDescription: String {
       return "StringUnicodeScalarView(\(self.description.debugDescription))"
     }

     @_versioned // FIXME(sil-serialize-all)
     internal var _core: _StringCore

     /// The offset of this view's `_core` from an original core. This works
     /// around the fact that `_StringCore` is always zero-indexed.
     /// `_coreOffset` should be subtracted from `UnicodeScalarIndex.encodedOffset`
     /// before that value is used as a `_core` index.
     @_versioned // FIXME(sil-serialize-all)
     internal var _coreOffset: Int
   }

   /// Creates a string corresponding to the given collection of Unicode
   /// scalars.
   ///
   /// You can use this initializer to create a new string from a slice of
   /// another string's `unicodeScalars` view.
   ///
   ///     let picnicGuest = "Deserving porcupine"
   ///     if let i = picnicGuest.unicodeScalars.index(of: " ") {
   ///         let adjective = String(picnicGuest.unicodeScalars[..<i])
   ///         print(adjective)
   ///     }
   ///     // Prints "Deserving"
   ///
   /// The `adjective` constant is created by calling this initializer with a
   /// slice of the `picnicGuest.unicodeScalars` view.
   ///
   /// - Parameter unicodeScalars: A collection of Unicode scalar values.
   @_inlineable // FIXME(sil-serialize-all)
   public init(_ unicodeScalars: UnicodeScalarView) {
     self.init(unicodeScalars._core)
   }

   /// The index type for a string's `unicodeScalars` view.
   public typealias UnicodeScalarIndex = UnicodeScalarView.Index
 }

 extension String.UnicodeScalarView : _SwiftStringView {
   @_inlineable // FIXME(sil-serialize-all)
   @_versioned // FIXME(sil-serialize-all)
   internal var _persistentContent : String { return String(_core) }
 }

 extension String {
   /// The string's value represented as a collection of Unicode scalar values.
   @_inlineable // FIXME(sil-serialize-all)
   public var unicodeScalars: UnicodeScalarView {
     get {
       return UnicodeScalarView(_core)
     }
     set {
       _core = newValue._core
     }
   }
 }

 extension String.UnicodeScalarView : RangeReplaceableCollection {
   /// Creates an empty view instance.
   @_inlineable // FIXME(sil-serialize-all)
   public init() {
     self = String.UnicodeScalarView(_StringCore())
   }

   /// Reserves enough space in the view's underlying storage to store the
   /// specified number of ASCII characters.
   ///
   /// Because a Unicode scalar value can require more than a single ASCII
   /// character's worth of storage, additional allocation may be necessary
   /// when adding to a Unicode scalar view after a call to
   /// `reserveCapacity(_:)`.
   ///
   /// - Parameter n: The minimum number of ASCII character's worth of storage
   ///   to allocate.
   ///
   /// - Complexity: O(*n*), where *n* is the capacity being reserved.
   @_inlineable // FIXME(sil-serialize-all)
   public mutating func reserveCapacity(_ n: Int) {
     _core.reserveCapacity(n)
   }

   /// Appends the given Unicode scalar to the view.
   ///
   /// - Parameter c: The character to append to the string.
   @_inlineable // FIXME(sil-serialize-all)
   public mutating func append(_ x: Unicode.Scalar) {
     _core.append(x)
   }

   /// Appends the Unicode scalar values in the given sequence to the view.
   ///
   /// - Parameter newElements: A sequence of Unicode scalar values.
   ///
   /// - Complexity: O(*n*), where *n* is the length of the resulting view.
   @_inlineable // FIXME(sil-serialize-all)
   public mutating func append<S : Sequence>(contentsOf newElements: S)
     where S.Element == Unicode.Scalar {
     _core.append(contentsOf: newElements.lazy.flatMap { $0.utf16 })
   }

   /// Replaces the elements within the specified bounds with the given Unicode
   /// scalar values.
   ///
   /// Calling this method invalidates any existing indices for use with this
   /// string.
   ///
   /// - Parameters:
   ///   - bounds: The range of elements to replace. The bounds of the range
   ///     must be valid indices of the view.
   ///   - newElements: The new Unicode scalar values to add to the string.
   ///
   /// - Complexity: O(*m*), where *m* is the combined length of the view and
   ///   `newElements`. If the call to `replaceSubrange(_:with:)` simply
   ///   removes elements at the end of the string, the complexity is O(*n*),
   ///   where *n* is equal to `bounds.count`.
   @_inlineable // FIXME(sil-serialize-all)
   public mutating func replaceSubrange<C>(
     _ bounds: Range<Index>,
     with newElements: C
   ) where C : Collection, C.Element == Unicode.Scalar {
     let rawSubRange: Range<Int> = _toCoreIndex(bounds.lowerBound) ..<
       _toCoreIndex(bounds.upperBound)
     let lazyUTF16 = newElements.lazy.flatMap { $0.utf16 }
     _core.replaceSubrange(rawSubRange, with: lazyUTF16)
   }
 }

 // Index conversions
 extension String.UnicodeScalarIndex {
   /// Creates an index in the given Unicode scalars view that corresponds
   /// exactly to the specified `UTF16View` position.
   ///
   /// The following example finds the position of a space in a string's `utf16`
   /// view and then converts that position to an index in the string's
   /// `unicodeScalars` view:
   ///
   ///     let cafe = "Café 🍵"
   ///
   ///     let utf16Index = cafe.utf16.index(of: 32)!
   ///     let scalarIndex = String.Index(utf16Index, within: cafe.unicodeScalars)!
   ///
   ///     print(String(cafe.unicodeScalars[..<scalarIndex]))
   ///     // Prints "Café"
   ///
   /// If the index passed as `sourcePosition` doesn't have an exact
   /// corresponding position in `unicodeScalars`, the result of the
   /// initializer is `nil`. For example, an attempt to convert the position of
   /// the trailing surrogate of a UTF-16 surrogate pair results in `nil`.
   ///
   /// - Parameters:
   ///   - sourcePosition: A position in the `utf16` view of a string. `utf16Index`
   ///     must be an element of `String(unicodeScalars).utf16.indices`.
   ///   - unicodeScalars: The `UnicodeScalarView` in which to find the new
   ///     position.
   @_inlineable // FIXME(sil-serialize-all)
   public init?(
     _ sourcePosition: String.UTF16Index,
     within unicodeScalars: String.UnicodeScalarView
   ) {
     if !unicodeScalars._isOnUnicodeScalarBoundary(sourcePosition) { return nil }
     self = sourcePosition
   }

   /// Returns the position in the given string that corresponds exactly to this
   /// index.
   ///
   /// This example first finds the position of a space (UTF-8 code point `32`)
   /// in a string's `utf8` view and then uses this method find the same position
   /// in the string.
   ///
   ///     let cafe = "Café 🍵"
   ///     let i = cafe.unicodeScalars.index(of: "🍵")
   ///     let j = i.samePosition(in: cafe)!
   ///     print(cafe[j...])
   ///     // Prints "🍵"
   ///
   /// - Parameter characters: The string to use for the index conversion.
   ///   This index must be a valid index of at least one view of `characters`.
   /// - Returns: The position in `characters` that corresponds exactly to
   ///   this index. If this index does not have an exact corresponding
   ///   position in `characters`, this method returns `nil`. For example,
   ///   an attempt to convert the position of a UTF-8 continuation byte
   ///   returns `nil`.
   @_inlineable // FIXME(sil-serialize-all)
   public func samePosition(in characters: String) -> String.Index? {
     return String.Index(self, within: characters)
   }
 }

 extension String.UnicodeScalarView {
   @_inlineable // FIXME(sil-serialize-all)
   @_versioned // FIXME(sil-serialize-all)
   internal func _isOnUnicodeScalarBoundary(_ i: Index) -> Bool {
     if _fastPath(_core.isASCII) { return true }
     if i == startIndex || i == endIndex {
       return true
     }
     if i._transcodedOffset != 0 { return false }
     let i2 = _toCoreIndex(i)
     if _fastPath(_core[i2] & 0xFC00 != 0xDC00) { return true }
     return _core[i2 &- 1] & 0xFC00 != 0xD800
   }

   // NOTE: Don't make this function inlineable.  Grapheme cluster
   // segmentation uses a completely different algorithm in Unicode 9.0.
   @_inlineable // FIXME(sil-serialize-all)
   @_versioned // FIXME(sil-serialize-all)
   internal func _isOnGraphemeClusterBoundary(_ i: Index) -> Bool {
     if i == startIndex || i == endIndex {
       return true
     }
     if !_isOnUnicodeScalarBoundary(i) { return false }
     let str = String(_core)
     return i == str.index(before: str.index(after: i))
   }
 }

 // Reflection
 extension String.UnicodeScalarView : CustomReflectable {
   /// Returns a mirror that reflects the Unicode scalars view of a string.
   @_inlineable // FIXME(sil-serialize-all)
   public var customMirror: Mirror {
     return Mirror(self, unlabeledChildren: self)
   }
 }

 extension String.UnicodeScalarView : CustomPlaygroundQuickLookable {
   @_inlineable // FIXME(sil-serialize-all)
   public var customPlaygroundQuickLook: PlaygroundQuickLook {
     return .text(description)
   }
 }

 // backward compatibility for index interchange.
 extension String.UnicodeScalarView {
   @_inlineable // FIXME(sil-serialize-all)
   @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 {
     return index(after: i!)
   }
   @_inlineable // FIXME(sil-serialize-all)
   @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 {
     return index(i!, offsetBy: n)
   }
   @_inlineable // FIXME(sil-serialize-all)
   @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 {
     return distance(from: i!, to: j!)
   }
   @_inlineable // FIXME(sil-serialize-all)
   @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 {
     return self[i!]
   }
 }

 //===--- 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 {
   public typealias SubSequence = Substring.UnicodeScalarView

   @_inlineable // FIXME(sil-serialize-all)
   @available(swift, introduced: 4)
   public subscript(r: Range<Index>) -> String.UnicodeScalarView.SubSequence {
     return String.UnicodeScalarView.SubSequence(self, _bounds: r)
   }

   /// Accesses the Unicode scalar values in the given range.
   ///
   /// The example below uses this subscript to access the scalar values up
   /// to, but not including, the first comma (`","`) in the string.
   ///
   ///     let str = "All this happened, more or less."
   ///     let i = str.unicodeScalars.index(of: ",")!
   ///     let substring = str.unicodeScalars[str.unicodeScalars.startIndex ..< i]
   ///     print(String(substring))
   ///     // Prints "All this happened"
   ///
   /// - Complexity: O(*n*) if the underlying string is bridged from
   ///   Objective-C, where *n* is the length of the string; otherwise, O(1).
   @_inlineable // FIXME(sil-serialize-all)
   @available(swift, obsoleted: 4)
   public subscript(r: Range<Index>) -> String.UnicodeScalarView {
     let rawSubRange = _toCoreIndex(r.lowerBound)..<_toCoreIndex(r.upperBound)
     return String.UnicodeScalarView(
       _core[rawSubRange], coreOffset: r.lowerBound.encodedOffset)
   }

   @_inlineable // FIXME(sil-serialize-all)
   @available(swift, obsoleted: 4)
   public subscript(bounds: ClosedRange<Index>) -> String.UnicodeScalarView {
     return self[bounds.relative(to: self)]
   }
 }
	//===----------------------------------------------------------------------===//
	//
	// This source file is part of the Swift.org open source project
	//
	// Copyright (c) 2014 - 2017 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
	//
	//===----------------------------------------------------------------------===//

	extension String {
	/// A view of a string's contents as a collection of Unicode scalar values.
	///
	/// You can access a string's view of Unicode scalar values by using its
	/// `unicodeScalars` property. Unicode scalar values are the 21-bit codes
	/// that are the basic unit of Unicode. Each scalar value is represented by
	/// a `Unicode.Scalar` instance and is equivalent to a UTF-32 code unit.
	///
	/// let flowers = "Flowers 💐"
	/// for v in flowers.unicodeScalars {
	/// print(v.value)
	/// }
	/// // 70
	/// // 108
	/// // 111
	/// // 119
	/// // 101
	/// // 114
	/// // 115
	/// // 32
	/// // 128144
	///
	/// Some characters that are visible in a string are made up of more than one
	/// Unicode scalar value. In that case, a string's `unicodeScalars` view
	/// contains more elements than the string itself.
	///
	/// let flag = "🇵🇷"
	/// for c in flag {
	/// print(c)
	/// }
	/// // 🇵🇷
	///
	/// for v in flag.unicodeScalars {
	/// print(v.value)
	/// }
	/// // 127477
	/// // 127479
	///
	/// You can convert a `String.UnicodeScalarView` instance back into a string
	/// using the `String` type's `init(_:)` initializer.
	///
	/// let favemoji = "My favorite emoji is 🎉"
	/// if let i = favemoji.unicodeScalars.index(where: { $0.value >= 128 }) {
	/// let asciiPrefix = String(favemoji.unicodeScalars[..<i])
	/// print(asciiPrefix)
	/// }
	/// // Prints "My favorite emoji is "
	@_fixed_layout // FIXME(sil-serialize-all)
	public struct UnicodeScalarView :
	BidirectionalCollection,
	CustomStringConvertible,
	CustomDebugStringConvertible
	{
	@_inlineable // FIXME(sil-serialize-all)
	@_versioned // FIXME(sil-serialize-all)
	internal init(_ _core: _StringCore, coreOffset: Int = 0) {
	self._core = _core
	self._coreOffset = coreOffset
	}

	@_fixed_layout // FIXME(sil-serialize-all)
	@_versioned // FIXME(sil-serialize-all)
	internal struct _ScratchIterator : IteratorProtocol {
	@_versioned
	internal var core: _StringCore
	@_versioned // FIXME(sil-serialize-all)
	internal var idx: Int
	@_inlineable // FIXME(sil-serialize-all)
	@_versioned // FIXME(sil-serialize-all)
	internal init(_ core: _StringCore, _ pos: Int) {
	self.idx = pos
	self.core = core
	}
	@_inlineable // FIXME(sil-serialize-all)
	@_versioned // FIXME(sil-serialize-all)
	@inline(__always)
	internal mutating func next() -> UTF16.CodeUnit? {
	if idx == core.endIndex {
	return nil
	}
	defer { idx += 1 }
	return self.core[idx]
	}
	}

	public typealias Index = String.Index

	/// Translates a `_core` index into a `UnicodeScalarIndex` using this view's
	/// `_coreOffset`.
	@_inlineable // FIXME(sil-serialize-all)
	@_versioned // FIXME(sil-serialize-all)
	internal func _fromCoreIndex(_ i: Int) -> Index {
	return Index(encodedOffset: i + _coreOffset)
	}

	/// Translates a `UnicodeScalarIndex` into a `_core` index using this view's
	/// `_coreOffset`.
	@_inlineable // FIXME(sil-serialize-all)
	@_versioned // FIXME(sil-serialize-all)
	internal func _toCoreIndex(_ i: Index) -> Int {
	return i.encodedOffset - _coreOffset
	}

	/// The position of the first Unicode scalar value if the string is
	/// nonempty.
	///
	/// If the string is empty, `startIndex` is equal to `endIndex`.
	@_inlineable // FIXME(sil-serialize-all)
	public var startIndex: Index {
	return _fromCoreIndex(_core.startIndex)
	}

	/// The "past the end" position---that is, the position one greater than
	/// the last valid subscript argument.
	///
	/// In an empty Unicode scalars view, `endIndex` is equal to `startIndex`.
	@_inlineable // FIXME(sil-serialize-all)
	public var endIndex: Index {
	return _fromCoreIndex(_core.endIndex)
	}

	/// Returns the next consecutive location after `i`.
	///
	/// - Precondition: The next location exists.
	@_inlineable // FIXME(sil-serialize-all)
	public func index(after i: Index) -> Index {
	let i = _toCoreIndex(i)
	var scratch = _ScratchIterator(_core, i)
	var decoder = UTF16()
	let (_, length) = decoder._decodeOne(&scratch)
	return _fromCoreIndex(i + length)
	}

	/// Returns the previous consecutive location before `i`.
	///
	/// - Precondition: The previous location exists.
	@_inlineable // FIXME(sil-serialize-all)
	public func index(before i: Index) -> Index {
	var i = _toCoreIndex(i) - 1
	let codeUnit = _core[i]
	if _slowPath((codeUnit >> 10) == 0b1101_11) {
	if i != 0 && (_core[i - 1] >> 10) == 0b1101_10 {
	i -= 1
	}
	}
	return _fromCoreIndex(i)
	}

	/// Accesses the Unicode scalar value at the given position.
	///
	/// The following example searches a string's Unicode scalars view for a
	/// capital letter and then prints the character and Unicode scalar value
	/// at the found index:
	///
	/// let greeting = "Hello, friend!"
	/// if let i = greeting.unicodeScalars.index(where: { "A"..."Z" ~= $0 }) {
	/// print("First capital letter: \(greeting.unicodeScalars[i])")
	/// print("Unicode scalar value: \(greeting.unicodeScalars[i].value)")
	/// }
	/// // Prints "First capital letter: H"
	/// // Prints "Unicode scalar value: 72"
	///
	/// - Parameter position: A valid index of the character view. `position`
	/// must be less than the view's end index.
	@_inlineable // FIXME(sil-serialize-all)
	public subscript(position: Index) -> Unicode.Scalar {
	var scratch = _ScratchIterator(_core, _toCoreIndex(position))
	var decoder = UTF16()
	switch decoder.decode(&scratch) {
	case .scalarValue(let us):
	return us
	case .emptyInput:
	_sanityCheckFailure("cannot subscript using an endIndex")
	case .error:
	return Unicode.Scalar(0xfffd)!
	}
	}

	/// An iterator over the Unicode scalars that make up a `UnicodeScalarView`
	/// collection.
	@_fixed_layout // FIXME(sil-serialize-all)
	public struct Iterator : IteratorProtocol {
	@_inlineable // FIXME(sil-serialize-all)
	@_versioned // FIXME(sil-serialize-all)
	internal init(_ _base: _StringCore) {
	self._iterator = _base.makeIterator()
	if _base.hasContiguousStorage {
	self._baseSet = true
	if _base.isASCII {
	self._ascii = true
	self._asciiBase = UnsafeBufferPointer(
	start: _base._baseAddress?.assumingMemoryBound(
	to: UTF8.CodeUnit.self),
	count: _base.count).makeIterator()
	} else {
	self._ascii = false
	self._base = UnsafeBufferPointer<UInt16>(
	start: _base._baseAddress?.assumingMemoryBound(
	to: UTF16.CodeUnit.self),
	count: _base.count).makeIterator()
	}
	} else {
	self._ascii = false
	self._baseSet = false
	}
	}

	/// Advances to the next element and returns it, or `nil` if no next
	/// element exists.
	///
	/// Once `nil` has been returned, all subsequent calls return `nil`.
	///
	/// - Precondition: `next()` has not been applied to a copy of `self`
	/// since the copy was made.
	@_inlineable // FIXME(sil-serialize-all)
	public mutating func next() -> Unicode.Scalar? {
	var result: UnicodeDecodingResult
	if _baseSet {
	if _ascii {
	switch self._asciiBase.next() {
	case let x?:
	result = .scalarValue(Unicode.Scalar(x))
	case nil:
	result = .emptyInput
	}
	} else {
	result = _decoder.decode(&(self._base!))
	}
	} else {
	result = _decoder.decode(&(self._iterator))
	}
	switch result {
	case .scalarValue(let us):
	return us
	case .emptyInput:
	return nil
	case .error:
	return Unicode.Scalar(0xfffd)
	}
	}
	@_versioned // FIXME(sil-serialize-all)
	internal var _decoder: UTF16 = UTF16()
	@_versioned // FIXME(sil-serialize-all)
	internal let _baseSet: Bool
	@_versioned // FIXME(sil-serialize-all)
	internal let _ascii: Bool
	@_versioned // FIXME(sil-serialize-all)
	internal var _asciiBase: UnsafeBufferPointerIterator<UInt8>!
	@_versioned // FIXME(sil-serialize-all)
	internal var _base: UnsafeBufferPointerIterator<UInt16>!
	@_versioned // FIXME(sil-serialize-all)
	internal var _iterator: IndexingIterator<_StringCore>
	}

	/// Returns an iterator over the Unicode scalars that make up this view.
	///
	/// - Returns: An iterator over this collection's `Unicode.Scalar` elements.
	@_inlineable // FIXME(sil-serialize-all)
	public func makeIterator() -> Iterator {
	return Iterator(_core)
	}

	@_inlineable // FIXME(sil-serialize-all)
	public var description: String {
	return String(_core)
	}

	@_inlineable // FIXME(sil-serialize-all)
	public var debugDescription: String {
	return "StringUnicodeScalarView(\(self.description.debugDescription))"
	}

	@_versioned // FIXME(sil-serialize-all)
	internal var _core: _StringCore

	/// The offset of this view's `_core` from an original core. This works
	/// around the fact that `_StringCore` is always zero-indexed.
	/// `_coreOffset` should be subtracted from `UnicodeScalarIndex.encodedOffset`
	/// before that value is used as a `_core` index.
	@_versioned // FIXME(sil-serialize-all)
	internal var _coreOffset: Int
	}

	/// Creates a string corresponding to the given collection of Unicode
	/// scalars.
	///
	/// You can use this initializer to create a new string from a slice of
	/// another string's `unicodeScalars` view.
	///
	/// let picnicGuest = "Deserving porcupine"
	/// if let i = picnicGuest.unicodeScalars.index(of: " ") {
	/// let adjective = String(picnicGuest.unicodeScalars[..<i])
	/// print(adjective)
	/// }
	/// // Prints "Deserving"
	///
	/// The `adjective` constant is created by calling this initializer with a
	/// slice of the `picnicGuest.unicodeScalars` view.
	///
	/// - Parameter unicodeScalars: A collection of Unicode scalar values.
	@_inlineable // FIXME(sil-serialize-all)
	public init(_ unicodeScalars: UnicodeScalarView) {
	self.init(unicodeScalars._core)
	}

	/// The index type for a string's `unicodeScalars` view.
	public typealias UnicodeScalarIndex = UnicodeScalarView.Index
	}

	extension String.UnicodeScalarView : _SwiftStringView {
	@_inlineable // FIXME(sil-serialize-all)
	@_versioned // FIXME(sil-serialize-all)
	internal var _persistentContent : String { return String(_core) }
	}

	extension String {
	/// The string's value represented as a collection of Unicode scalar values.
	@_inlineable // FIXME(sil-serialize-all)
	public var unicodeScalars: UnicodeScalarView {
	get {
	return UnicodeScalarView(_core)
	}
	set {
	_core = newValue._core
	}
	}
	}

	extension String.UnicodeScalarView : RangeReplaceableCollection {
	/// Creates an empty view instance.
	@_inlineable // FIXME(sil-serialize-all)
	public init() {
	self = String.UnicodeScalarView(_StringCore())
	}

	/// Reserves enough space in the view's underlying storage to store the
	/// specified number of ASCII characters.
	///
	/// Because a Unicode scalar value can require more than a single ASCII
	/// character's worth of storage, additional allocation may be necessary
	/// when adding to a Unicode scalar view after a call to
	/// `reserveCapacity(_:)`.
	///
	/// - Parameter n: The minimum number of ASCII character's worth of storage
	/// to allocate.
	///
	/// - Complexity: O(n), where n is the capacity being reserved.
	@_inlineable // FIXME(sil-serialize-all)
	public mutating func reserveCapacity(_ n: Int) {
	_core.reserveCapacity(n)
	}

	/// Appends the given Unicode scalar to the view.
	///
	/// - Parameter c: The character to append to the string.
	@_inlineable // FIXME(sil-serialize-all)
	public mutating func append(_ x: Unicode.Scalar) {
	_core.append(x)
	}

	/// Appends the Unicode scalar values in the given sequence to the view.
	///
	/// - Parameter newElements: A sequence of Unicode scalar values.
	///
	/// - Complexity: O(n), where n is the length of the resulting view.
	@_inlineable // FIXME(sil-serialize-all)
	public mutating func append<S : Sequence>(contentsOf newElements: S)
	where S.Element == Unicode.Scalar {
	_core.append(contentsOf: newElements.lazy.flatMap { $0.utf16 })
	}

	/// Replaces the elements within the specified bounds with the given Unicode
	/// scalar values.
	///
	/// Calling this method invalidates any existing indices for use with this
	/// string.
	///
	/// - Parameters:
	/// - bounds: The range of elements to replace. The bounds of the range
	/// must be valid indices of the view.
	/// - newElements: The new Unicode scalar values to add to the string.
	///
	/// - Complexity: O(m), where m is the combined length of the view and
	/// `newElements`. If the call to `replaceSubrange(_:with:)` simply
	/// removes elements at the end of the string, the complexity is O(n),
	/// where n is equal to `bounds.count`.
	@_inlineable // FIXME(sil-serialize-all)
	public mutating func replaceSubrange<C>(
	_ bounds: Range<Index>,
	with newElements: C
	) where C : Collection, C.Element == Unicode.Scalar {
	let rawSubRange: Range<Int> = _toCoreIndex(bounds.lowerBound) ..<
	_toCoreIndex(bounds.upperBound)
	let lazyUTF16 = newElements.lazy.flatMap { $0.utf16 }
	_core.replaceSubrange(rawSubRange, with: lazyUTF16)
	}
	}

	// Index conversions
	extension String.UnicodeScalarIndex {
	/// Creates an index in the given Unicode scalars view that corresponds
	/// exactly to the specified `UTF16View` position.
	///
	/// The following example finds the position of a space in a string's `utf16`
	/// view and then converts that position to an index in the string's
	/// `unicodeScalars` view:
	///
	/// let cafe = "Café 🍵"
	///
	/// let utf16Index = cafe.utf16.index(of: 32)!
	/// let scalarIndex = String.Index(utf16Index, within: cafe.unicodeScalars)!
	///
	/// print(String(cafe.unicodeScalars[..<scalarIndex]))
	/// // Prints "Café"
	///
	/// If the index passed as `sourcePosition` doesn't have an exact
	/// corresponding position in `unicodeScalars`, the result of the
	/// initializer is `nil`. For example, an attempt to convert the position of
	/// the trailing surrogate of a UTF-16 surrogate pair results in `nil`.
	///
	/// - Parameters:
	/// - sourcePosition: A position in the `utf16` view of a string. `utf16Index`
	/// must be an element of `String(unicodeScalars).utf16.indices`.
	/// - unicodeScalars: The `UnicodeScalarView` in which to find the new
	/// position.
	@_inlineable // FIXME(sil-serialize-all)
	public init?(
	_ sourcePosition: String.UTF16Index,
	within unicodeScalars: String.UnicodeScalarView
	) {
	if !unicodeScalars._isOnUnicodeScalarBoundary(sourcePosition) { return nil }
	self = sourcePosition
	}

	/// Returns the position in the given string that corresponds exactly to this
	/// index.
	///
	/// This example first finds the position of a space (UTF-8 code point `32`)
	/// in a string's `utf8` view and then uses this method find the same position
	/// in the string.
	///
	/// let cafe = "Café 🍵"
	/// let i = cafe.unicodeScalars.index(of: "🍵")
	/// let j = i.samePosition(in: cafe)!
	/// print(cafe[j...])
	/// // Prints "🍵"
	///
	/// - Parameter characters: The string to use for the index conversion.
	/// This index must be a valid index of at least one view of `characters`.
	/// - Returns: The position in `characters` that corresponds exactly to
	/// this index. If this index does not have an exact corresponding
	/// position in `characters`, this method returns `nil`. For example,
	/// an attempt to convert the position of a UTF-8 continuation byte
	/// returns `nil`.
	@_inlineable // FIXME(sil-serialize-all)
	public func samePosition(in characters: String) -> String.Index? {
	return String.Index(self, within: characters)
	}
	}

	extension String.UnicodeScalarView {
	@_inlineable // FIXME(sil-serialize-all)
	@_versioned // FIXME(sil-serialize-all)
	internal func _isOnUnicodeScalarBoundary(_ i: Index) -> Bool {
	if _fastPath(_core.isASCII) { return true }
	if i == startIndex \|\| i == endIndex {
	return true
	}
	if i._transcodedOffset != 0 { return false }
	let i2 = _toCoreIndex(i)
	if _fastPath(_core[i2] & 0xFC00 != 0xDC00) { return true }
	return _core[i2 &- 1] & 0xFC00 != 0xD800
	}

	// NOTE: Don't make this function inlineable. Grapheme cluster
	// segmentation uses a completely different algorithm in Unicode 9.0.
	@_inlineable // FIXME(sil-serialize-all)
	@_versioned // FIXME(sil-serialize-all)
	internal func _isOnGraphemeClusterBoundary(_ i: Index) -> Bool {
	if i == startIndex \|\| i == endIndex {
	return true
	}
	if !_isOnUnicodeScalarBoundary(i) { return false }
	let str = String(_core)
	return i == str.index(before: str.index(after: i))
	}
	}

	// Reflection
	extension String.UnicodeScalarView : CustomReflectable {
	/// Returns a mirror that reflects the Unicode scalars view of a string.
	@_inlineable // FIXME(sil-serialize-all)
	public var customMirror: Mirror {
	return Mirror(self, unlabeledChildren: self)
	}
	}

	extension String.UnicodeScalarView : CustomPlaygroundQuickLookable {
	@_inlineable // FIXME(sil-serialize-all)
	public var customPlaygroundQuickLook: PlaygroundQuickLook {
	return .text(description)
	}
	}

	// backward compatibility for index interchange.
	extension String.UnicodeScalarView {
	@_inlineable // FIXME(sil-serialize-all)
	@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 {
	return index(after: i!)
	}
	@_inlineable // FIXME(sil-serialize-all)
	@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 {
	return index(i!, offsetBy: n)
	}
	@_inlineable // FIXME(sil-serialize-all)
	@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 {
	return distance(from: i!, to: j!)
	}
	@_inlineable // FIXME(sil-serialize-all)
	@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 {
	return self[i!]
	}
	}

	//===--- 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 {
	public typealias SubSequence = Substring.UnicodeScalarView

	@_inlineable // FIXME(sil-serialize-all)
	@available(swift, introduced: 4)
	public subscript(r: Range<Index>) -> String.UnicodeScalarView.SubSequence {
	return String.UnicodeScalarView.SubSequence(self, _bounds: r)
	}

	/// Accesses the Unicode scalar values in the given range.
	///
	/// The example below uses this subscript to access the scalar values up
	/// to, but not including, the first comma (`","`) in the string.
	///
	/// let str = "All this happened, more or less."
	/// let i = str.unicodeScalars.index(of: ",")!
	/// let substring = str.unicodeScalars[str.unicodeScalars.startIndex ..< i]
	/// print(String(substring))
	/// // Prints "All this happened"
	///
	/// - Complexity: O(n) if the underlying string is bridged from
	/// Objective-C, where n is the length of the string; otherwise, O(1).
	@_inlineable // FIXME(sil-serialize-all)
	@available(swift, obsoleted: 4)
	public subscript(r: Range<Index>) -> String.UnicodeScalarView {
	let rawSubRange = _toCoreIndex(r.lowerBound)..<_toCoreIndex(r.upperBound)
	return String.UnicodeScalarView(
	_core[rawSubRange], coreOffset: r.lowerBound.encodedOffset)
	}

	@_inlineable // FIXME(sil-serialize-all)
	@available(swift, obsoleted: 4)
	public subscript(bounds: ClosedRange<Index>) -> String.UnicodeScalarView {
	return self[bounds.relative(to: self)]
	}
	}