title: XCode Mach-O linker error
body: <p>After upgrading to XCode 4.5 GM from XCode 4.3 + llvm 3.1, I start getting the following linker errors.
  I have verified that the static library where  "_InvokeBridge" is defined is linked correctly.</p>
  
  <p>Any idea what might cause the error? Also, Are there tips to investigate Mach-o linker error in general?</p>
  
  <pre><code>undefined symbols for architecture i386:
    "void     pplx::details::_UnrealizedChore::_InvokeBridge&lt;pplx::details::_PPLTaskHandle&lt;std::__1::shared_ptr&lt;BI::Url const&gt;, pplx::task&lt;std::__1::shared_ptr&lt;BI::Url const&gt; &gt;::_InitialTaskHandle&lt;std::__1::shared_ptr&lt;BI::Url const&gt;, BI::ServicesDocumentSession::GetViewUriAsync()::$_3, pplx::details::_TypeSelectorNoAsync&gt;, pplx::details::_UnrealizedChore&gt; &gt;(pplx::details::_PPLTaskHandle&lt;std::__1::shared_ptr&lt;BI::Url const&gt;, pplx::task&lt;std::__1::shared_ptr&lt;BI::Url const&gt; &gt;::_InitialTaskHandle&lt;std::__1::shared_ptr&lt;BI::Url const&gt;, BI::ServicesDocumentSession::GetViewUriAsync()::$_3, pplx::details::_TypeSelectorNoAsync&gt;, pplx::details::_UnrealizedChore&gt;*)", referenced from:
    pplx::details::_PPLTaskHandle&lt;std::__1::shared_ptr&lt;BI::Url const&gt;, pplx::task&lt;std::__1::shared_ptr&lt;BI::Url const&gt; &gt;::_InitialTaskHandle&lt;std::__1::shared_ptr&lt;BI::Url const&gt;, BI::ServicesDocumentSession::GetViewUriAsync()::$_3, pplx::details::_TypeSelectorNoAsync&gt;, pplx::details::_UnrealizedChore&gt;::_PPLTaskHandle(std::__1::shared_ptr&lt;pplx::details::_Task_impl&lt;std::__1::shared_ptr&lt;BI::Url const&gt; &gt; &gt; const&amp;) in libDataPlatform.a(ServicesDocumentSession.o)
  </code></pre>
  
  <p>thank you much,
  A</p>