title: boost::unordered_map -- Need to specify a custom hash function for hashing std::set<int>?
body: <p>I'd like use <code>boost::unordered_map&lt;key,value&gt;</code>, where <code>key</code> is a <code>std::set&lt;int&gt;</code>. Since a set of integers is no built-in type, I assumed I had to supply my own hash function (or, rather, I was thinking of using <a href="http://www.boost.org/doc/libs/1_35_0/doc/html/boost/hash_range_id420926.html" rel="nofollow">boost's hash_range</a>). </p>
  
  <p>However, now I tried initializing a hash map like this, neither supplying a hash function nor an equality predicate -- and gcc didn't complain. What is happening here? Is boost clever enough to hash STL containers all on its own? Is this going to be slower than if I used a custom hash function? What about using <code>boost::hash_range</code>?</p>
  
  <p>Thanks in advance.</p>