   public init(
     bufferClass: AnyClass,
     minimumCapacity: Int,
-    initialHeader: @noescape (buffer: AnyObject, capacity: @noescape (AnyObject) -> Int) throws -> Header
+    makingHeaderWith factory:
+      (buffer: AnyObject, capacity: (AnyObject) -> Int) throws -> Header
   ) rethrows {
-    self = ManagedBufferPointer(bufferClass: bufferClass, minimumCapacity: minimumCapacity)
+    self = ManagedBufferPointer(
+      bufferClass: bufferClass, minimumCapacity: minimumCapacity)
 
     // initialize the header field
     try withUnsafeMutablePointerToHeader {
       $0.initialize(with: 
-        try initialHeader(
+        try factory(
           buffer: self.buffer,
           capacity: {
             ManagedBufferPointer(unsafeBufferObject: $0).capacity


  /// Destroy the stored Header.
  deinit {
    ManagedBufferPointer(self).withUnsafeMutablePointerToHeader { $0.deinitialize() }
  }

  /// The stored `Header` instance.
  public final var header: Header {
    addressWithNativeOwner {
      return (
        ManagedBufferPointer(self).withUnsafeMutablePointerToHeader { UnsafePointer($0) },
        Builtin.castToNativeObject(self))
    }
    mutableAddressWithNativeOwner {

  : ManagedProtoBuffer<Header, Element> {

  /// Create a new instance of the most-derived class, calling
  /// `factory` on the partially-constructed object to generate
  /// an initial `Header`.
  public final class func create(
    minimumCapacity: Int,
    makingHeaderWith factory: (
      ManagedProtoBuffer<Header, Element>) throws -> Header
  ) rethrows -> ManagedBuffer<Header, Element> {

    let p = try ManagedBufferPointer<Header, Element>(
      bufferClass: self,
      minimumCapacity: minimumCapacity,
      makingHeaderWith: { buffer, _ in
        try factory(
          unsafeDowncast(buffer, to: ManagedProtoBuffer<Header, Element>.self))
      })

