title: PHP curly brace syntax for member variable
body: <p>First question on SO and it's a real RTM candidate. But I promise you I've looked and can't seem to find it. I'll happily do a #headpalm when it turns out to be a simple thing that I missed.</p>
  
  <p>Trying to figure out Zend Framework and came across the following syntax:</p>
  
  <pre><code>$this-&gt;_session-&gt;{'user_id'}
  </code></pre>
  
  <p>I have never seen the curly braces syntax used to access what appears to be a member variable. How is it different than</p>
  
  <pre><code>$this-&gt;_session-&gt;user_id
  </code></pre>
  
  <p>I'm assuming that the _session is irrelevant, but including it in the question since it may not be.</p>
  
  <p>Are the curly braces just a cleanliness convention that attempts to wrap the compound variable name user_id? Or is it some kind of a special accessor?</p>
  
  <p>Any pointers into TFM so I can R up would be humbly appreciated.</p>
  
  <p>Many thanks. Please be gentle.</p>