title: Hash "has_key" complexity in Ruby
body: <p>I have a hash <code>vars = {"a" =&gt; "Name", "b" =&gt; "Address" , "c" =&gt; "Phone"}</code>. I want to check the performance of this line :</p>
  
  <pre><code>vars.has_key(:b)?
  </code></pre>
  
  <p>Is it O(1) or O(size of hash) ?</p>