title: How to directly use key as hash for std::unordered_map?
body: <p>The keys in my <code>std::unordered_map</code> are <a href="http://www.boost.org/doc/libs/1_42_0/libs/uuid/uuid.html" rel="nofollow"><code>boost::uuids::uuid</code></a>s, thus 128 bit hashes considered unique. However, the compiler can't know that and therefore says this.</p>
  
  <pre><code>error C2338: The C++ Standard doesn't provide a hash for this type.
  </code></pre>
  
  <p>How can I make the map use the keys as hashes as they are? By the way, <code>std::size_t</code> is defined as <code>unsigned int __w64</code> on my system, which I think refers to only 64 bits.</p>