title: Casting between different UnsafePointer<T> in swift
body: <p>I am trying to use a C-Api from swift. As an example the C-Api goes this ways:</p>
  
  <pre><code>void doThingsOnRawData(const unsigned char* data);
  </code></pre>
  
  <p>Swift converts this to:</p>
  
  <pre><code>void doThingsOnRawData(UnsafePointer&lt;UInt8&gt;);
  </code></pre>
  
  <p>Now I want to pass the data from an NSData to the function. NSData.byte returns the type:</p>
  
  <pre><code>UnsafePointer&lt;()&gt;
  </code></pre>
  
  <ol>
  <li><p>Is this some kind of void* type? </p></li>
  <li><p>At least swift won't accept it as an <code>UnsafePointer&lt;UInt8&gt;</code>. What do I do to cast this?</p></li>
  </ol>