title: What is the Ruby way to determine if an array has only unique entries?
body: <p>I want to find out if an <code>Array</code> contains only unique (distinct) entries.</p>
  
  <pre><code>[1,2,3,2].what_goes_here? #=&gt; false
  [1,2,3,4].what_goes_here? #=&gt; true
  </code></pre>
  
  <p>I don't want to manipulate the original array, so </p>
  
  <blockquote>
    <p>uniq! { |item| ... } → ary or nil
    ...
    Returns nil if no changes are made (that is, no duplicates are found).</p>
  </blockquote>
  
  <p>seems not the right solution. Otherwise I could probably do <code>[1,2,3,4].uniq!.nil?</code>.</p>
  
  <p>I prefer an elegant, readable, over a convoluted-but-better-performing solution.</p>