title: How to you distinguish a symbol table from a regular hash variable?
body: <p>Is there any way to tell whether a hash reference is referring to a symbol table? </p>
  
  <p>That is, how could the function</p>
  
  <pre><code>sub foo {
      my ($hashref) = @_;
      ...
  }
  </code></pre>
  
  <p>know whether it had been invoked as </p>
  
  <pre><code>foo( \%main:: )
  </code></pre>
  
  <p>rather than</p>
  
  <pre><code>foo( \%main )
  </code></pre>
  
  <p>? </p>
  
  <p>The application is a function that sometimes <code>tie</code>'s hash variables, but I'd want to avoid trying to tie a symbol table.</p>