title: How to enable ARC for a single file
body: <p>I want to bring a single Objective-C class written using ARC into an old project. The internet provides many references for how to enable ARC for your project and then disable it for single files but I want to do the opposite. </p>
  
  <p>I want to leave the project as it is, i.e. using manual reference counting, and then enable ARC just for the new file. (My searches have failed me here.)</p>
  
  <p>Is this possible? How?</p>