Why does std::random_device define its copy constructor as deleted?
<p>The copy constructor for <code>std::random_device</code> is deleted, and I have no idea why.</p>

<p>The only note I found from the <a href="http://en.cppreference.com/w/cpp/numeric/random/random_device/random_device">docs</a> is:</p>

<blockquote>
  <p>2) The copy constructor is deleted: <code>std::random_device</code> is not copyable.</p>
</blockquote>

<p>There doesn't seem to be a clear reason for why it is deleted. What is the reason behind this?</p>