title: Why does Box<[T]> need 16 bytes in memory, but a referenced slice needs only 8? (on x64 machine)
body: <p>Consider:</p>
  
  <pre class="lang-rust prettyprint-override"><code>fn main() {
      // Prints 8, 8, 16
      println!(
          "{}, {}, {}",
          std::mem::size_of::&lt;Box&lt;i8&gt;&gt;(),
          std::mem::size_of::&lt;Box&lt;&amp;[i8]&gt;&gt;(),
          std::mem::size_of::&lt;Box&lt;[i8]&gt;&gt;(),
      );
  }
  </code></pre>
  
  <p>Why do owned slices take 16 bytes, but referenced slices take only 8?</p>