title: can not type cast @selector expression when using setAction:(SEL)@selector(start:)
body: <p>I'm reading a project code from others, it could be compiled successfully in 32bit, but when I  switch the project to 64bit, there is one error message just like the title said.</p>
  
  <p>code:</p>
  
  <pre><code>[obj setAction:(SEL)@selector(start:)];
  </code></pre>
  
  <p>I know the return value type of <code>@selector</code> is <code>SEL</code> and the parameter of <code>setAction</code> needs a <code>SEL</code> args, but why it failed in 64bit?  What's the <code>SEL</code> type actually?</p>
  
  <p>Thanks!</p>