title: What does PHP do with strings to numbers when used as array keys?
body: <p>I'm trying to create an associative array like this:</p>
  
  <pre><code>$key = '0'
  $arr = array((string)$key=&gt;$value);
  </code></pre>
  
  <p>Later, checking <code>is_string(array_keys($arr)[0])</code> returns <code>false</code>.</p>
  
  <p>The casting didn't help, using " instead of ' didn't help.</p>
  
  <p>Am I doing something wrong, or is there another way around this, or is it impossible to have a numeric string array key?</p>