title: Ruby - can't modify frozen string (TypeError)
body: <p>Got</p>
  <blockquote>
  <p>... '[]=': can't modify frozen string (TypeError)</p>
  </blockquote>
  <p>when trying to modify what I thought was a copy of ARGV[0].</p>
  <p>Same results for each of</p>
  <pre><code>arg = ARGV[ 0 ]
  arg_cloned = ARGV[ 0 ].clone
  arg_to_s = ARGV[ 0 ].to_s
  
  arg[ 'x' ] = 'y'
  arg_cloned[ 'x' ] = 'y'
  arg_to_s[ 'x' ] = 'y'
  </code></pre>