   @inlinable
   public var utf16: UTF16View {
     get {
-      return base.utf16[startIndex..<endIndex]
+      // No need for index validation
+      UTF16View(base.utf16, _bounds: _bounds)
     }
     set {
       self = Substring(newValue)

  /// - Complexity: O(N), where N is the length of the resulting `String`'s
  ///   UTF-16.
  public init?(_ codeUnits: Substring.UTF16View) {
    let guts = codeUnits._slice._base._guts
    guard guts.isOnUnicodeScalarBoundary(codeUnits._slice.startIndex),
          guts.isOnUnicodeScalarBoundary(codeUnits._slice.endIndex) else {
      return nil
    }


  @inlinable
  public var unicodeScalars: UnicodeScalarView {
    get {
      // No need to validate any indices.
      UnicodeScalarView(_unchecked: base.unicodeScalars, bounds: _bounds)
    }
    set {
      self = Substring(newValue)
