   @inlinable
   public var unicodeScalars: UnicodeScalarView {
     get {
-      return base.unicodeScalars[startIndex..<endIndex]
+      // No need to validate any indices.
+      UnicodeScalarView(_unchecked: base.unicodeScalars, bounds: _bounds)
     }
     set {
       self = Substring(newValue)

    internal var _slice: Slice<String.UnicodeScalarView>

    /// Creates an instance that slices `base` at `_bounds`.
    internal init(
      _unchecked base: String.UnicodeScalarView, bounds: Range<Index>
    ) {

  ///
  /// - Complexity: O(1)
  public init(_ content: UTF8View) {
    // Note: We can trust that `content`'s bounds are valid, but they may not be
    // scalar aligned.
    let lower = content._wholeGuts.scalarAlign(content.startIndex)
    let upper = content._wholeGuts.scalarAlign(content.endIndex)
    let bounds = Range(_uncheckedBounds: (lower, upper))
    self.init(_unchecked: content._wholeGuts, bounds: bounds)
  }
}

