title: Call to implicitly-deleted default constructor of 'unordered_set< vector<int> >'
body: <p>It seems like when I try to define an unordered_set of vector, I get an error saying: &quot;Call to implicitly-deleted default constructor of <code>unordered_set&lt; vector&lt;int&gt; &gt;</code> .&quot; This doesn't happen when I define a regular (ordered) set: <code>set&lt; vector&lt;int&gt; &gt;</code>. It seems like I need to define <code>hash&lt;vector&lt;int&gt;&gt;</code> in order to get rid of the error.</p>
  <p>Does anyone know why I get this error only when I use <code>unordered_set</code>? Shouldn't both data structures use hashing, so why would an unordered_set need a custom-defined hash function? In fact, shouldn't a regular (ordered) <code>set</code> need some custom-defined comparator as well in order to order the <code>vector&lt;int&gt;</code> data structures?</p>