title: How to require ARC in a class?
body: <p>I have an app with both ARC code and non-ARC code. The compiler will catch when I try to compile non-ARC code as ARC. How do I cause a compile time error/notice when my ARC code is erroneously compiled without ARC? Obviously, the code will compile. It will just leak. The static analyzer will catch the problem. I would rather find a way to leave a pragma or define in my ARC code.</p>
  
  <p>The following is defined by Apple in <code>objc-api.h</code>:</p>
  
  <pre><code>/* OBJC_ARC_UNAVAILABLE: unavailable with -fobjc-arc */
  #if !defined(OBJC_ARC_UNAVAILABLE)
  #   if __has_feature(objc_arr)
  #       define OBJC_ARC_UNAVAILABLE __attribute__((unavailable("not available in automatic reference counting mode")))
  #   else
  #       define OBJC_ARC_UNAVAILABLE
  #   endif
  #endif
  </code></pre>
  
  <p>My C-macro-fu is weak. How would I use it? Or, perhaps there is a better symbol to check?</p>
  
  <p>P.S. I ask because I build much of my app from reusable libraries. I want to ensure that each file is compiled in the right way.</p>