title: SWIFT Apple Mach-O Linker Error "_OBJC_CLASS_$_BFExectur"
body: <p>Trying to use Parse with X-code and objective C.  4 different errors pop up.  Suggestions?</p>
  
  <pre><code>Undefined symbols for architecture x86_64:
    "_OBJC_CLASS_$_BFExecutor", referenced from:
      objc-class-ref in Parse(BFTask+Private.o)
      l_OBJC_$_CATEGORY_BFExecutor_$_Background in Parse(BFTask+Private.o)
    "_OBJC_CLASS_$_BFTask", referenced from:
      objc-class-ref in Parse(PSObject.o)
      objc-class-ref in Parse(PFFile.o)
      objc-class-ref in Parse(PFNetworkCommandRunner.o)
      objc-class-ref in Parse(PFQuery.o)
      objc-class-ref in Parse(PFRetryingCommandRunner.o)
      objc-class-ref in Parse(PFTaskQueue.o)
      objc-class-ref in Parse(PFUser.o)
      ...
    "_OBJC_CLASS_$_BFTaskCompletionSource", referenced from:
      objc-class-ref in Parse(PFObject.o)
      objc-class-ref in Parse(PFCommandCache.o)
      objc-class-ref in Parse(PFFile.o)
      objc-class-ref in Parse(PFNetworkCommandRunner.o)
      objc-class-ref in Parse(BFTask+Private.o)
  ld: symbol(s) not found for architecture x86_64
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  </code></pre>