   /// - Returns: The next element in the underlying sequence if a next element
   ///   exists; otherwise, `nil`.
   @_inlineable
+  @inline(__always)
   public mutating func next() -> Elements._Element? {
     if _position == _elements.endIndex { return nil }
     let element = _elements[_position]
     _elements.formIndex(after: &_position)
     return element
   }
+  
   @_versioned
   internal let _elements: Elements
   @_versioned

> : IteratorProtocol, Sequence {

  @_inlineable
  /// Creates an iterator over the given collection.
  public /// @testable
  init(_elements: Elements) {

  }

  @_inlineable
  @inline(__always)
  /// Creates an iterator over the given collection.
  public /// @testable
  init(_elements: Elements, _position: Elements.Index) {
