title: How to initialize a variable with a tidyselect helper?
body: <p>I'm using tidyselection in some function, and I have to concatenate the first argument with the ellipsis as it could be a specific class that would need a specific treatment.</p>
  
  <p>The normal behavior is this:</p>
  
  <pre><code>foo = function(x, ...){
      xloc = eval_select(expr(c(x, ...)), data = iris)
      return(xloc)
  }
  foo(everything())
  </code></pre>
  
  <p>I want to have <code>everything()</code> as the default value when <code>x</code> is <code>NULL</code> (<strong>I cannot put it directly in the header for some reason</strong>).</p>
  
  <p>Unfortunately, this syntax is not allowed:</p>
  
  <pre><code>bar = function(x, ...){
      if(is_null(x))
          x=everything() #throws an error
      xloc = eval_select(expr(c(x, ...)), data = iris)
      return(xloc)
  }
  bar(NULL)
  # Error: `everything()` must be used within a *selecting* function.
  # i See &lt;https://tidyselect.r-lib.org/reference/faq-selection-context.html&gt;.
  </code></pre>
  
  <p>I tried to wrap <code>everything()</code> with all "mystic" functions I know: <code>parse</code>, <code>deparse</code>, <code>call</code>, <code>substitute</code>, <code>quo</code>, <code>sym</code>, <code>enquo</code>, <code>ensym</code>, ... Nothing worked (you can see here that I don't master these very well).</p>
  
  <p><strong>With what expression can I replace my <code>x=everything()</code> line in my second code chunk for this function to work?</strong></p>
  
  <p><strong>Versions:</strong></p>
  
  <ul>
  <li>tidyselect version 1.0.0</li>
  <li>rlang version 0.4.5</li>
  <li>dplyr version 0.8.5</li>
  </ul>