What is “object of type ‘closure’ is not subsettable” error in Shiny? : <p>I have a shiny app and when I run it I get an error saying that an <code>object of type ‘closure’ is not subsettable</code>. What is that and how can I fix it?</p>

<p><strong>Note</strong>: I wrote this question as this comes up a lot, and the possible dupes are either not <code>shiny</code> related or so specific that it is not obvious that the answers are broadly applicable.</p>
