title: Cannot subscript a value of type 'String' with an index of type 'String.Index'
body: <p>Cannot subscript a value of type <code>String</code> with an index of type <code>String.Index</code></p>
  
  <pre><code>if let x = formulars.firstIndex(of: "("){
                  formulars[x] = ""
              }
  </code></pre>