title: Converting 2d fixed sized array to a slice
body: <p>With a 1 dimensional array it is possible to convert from a fixed sized array to a slice but is this possible with 2d array in a trivial way?</p>
  
  <pre><code>fn foo(r: &amp;[&amp;[usize]]) { }
  let r = [[0usize; 10]; 10];
  foo(&amp;r); //&lt;== error expected type `&amp;[&amp;[usize]]` found type `&amp;[[usize; 10]; 10]`
  </code></pre>