   // MARK: Implementation detail
 
   internal final override class var kind: Kind { return .reference }
-  
-  internal final override func _projectMutableAddress(
-    from base: UnsafePointer<Root>
-  ) -> (pointer: UnsafeMutablePointer<Value>, owner: AnyObject?) {
-    // Since we're a ReferenceWritableKeyPath, we know we don't mutate the base
-    // in practice.
-    return _projectMutableAddress(from: base.pointee)
-  }
   
   @usableFromInline
   internal final func _projectMutableAddress(from origBase: Root)

  
  // Prevent normal initialization. We use tail allocation via
  // allocWithTailElems().
  internal init() {
    _internalInvariantFailure("use _create(...)")
  }

    return result
  }
  
  final internal func withBuffer<T>(_ f: (KeyPathBuffer) throws -> T) rethrows -> T {
    defer { _fixLifetime(self) }
    
    let base = UnsafeRawPointer(Builtin.projectTailElems(self, Int32.self))
