title: Built in way to concatenate two Enumerators
body: <p>Say you have:</p>
  <pre><code>enum1 = 1.upto(5)
  enum2 = 7.upto(10)
  </code></pre>
  <p>I want:</p>
  <pre><code>enum_combined = enum1.some_method(enum2)
  </code></pre>
  <p>such that:</p>
  <pre><code>enum_combined.to_a #=&gt; [1, 2, 3, 4, 5, 7, 8, 9, 10]
  </code></pre>
  <p>I don't see any method on the Enumerator class that would do this, but before rolling my own solution I'd like make sure I'm not missing some built-in way to do this.</p>
  <p>To be clear: I want the returned result to be another <code>Enumerator</code> object, since I want the entire calculation to be lazy.</p>
  <h2>UPDATE</h2>
  <p>Per the linked duplicate, the way to achieve this is:</p>
  <pre><code>combined = [enum1, enum2].lazy.flat_map(&amp;:lazy)
  </code></pre>