title: Using set.insert( key ) as a conditional?
body: <p>I am trying to use <code>set.insert (key)</code> as a conditional, where if the key is inserted correctly (meaning that the key does NOT already exist in the set ) then it should go on and perform some kind of code. For example, something like:</p>
  
  <pre><code>if (set.insert( key )) {
      // some kind of code
  }
  </code></pre>
  
  <p>Is this allowed? Because the compiler is throwing this error: </p>
  
  <pre><code>conditional expression of type 'std::_Tree&lt;_Traits&gt;::iterator' is illegal
  </code></pre>