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copied!<p><code>Free</code> has some special logic: it checks to see whether <code>Self</code> is <code>nil</code>, and if so, it returns without doing anything -- so you can safely call <code>X.Free</code> even if <code>X</code> is <code>nil</code>. This is important when you're writing destructors -- David has more details in <a href="https://stackoverflow.com/a/8550628/87399">his answer</a>.</p> <p>You can look at the source code for <code>Free</code> to see how it works. I don't have the Delphi source handy, but it's something like this:</p> <pre><code>procedure TObject.Free; begin if Self <> nil then Destroy; end; </code></pre> <p>Or, if you prefer, you could think of it as the equivalent code using <a href="http://docwiki.embarcadero.com/VCL/en/System.Assigned" rel="nofollow noreferrer"><code>Assigned</code></a>:</p> <pre><code>procedure TObject.Free; begin if Assigned(Self) then Destroy; end; </code></pre> <p>You can write your own methods that check for <code>if Self <> nil</code>, as long as they're <a href="http://docwiki.embarcadero.com/RADStudio/en/Methods#Static_Methods" rel="nofollow noreferrer">static (i.e., not <code>virtual</code> or <code>dynamic</code>) instance methods</a> (thanks to David Heffernan for the documentation link). But in the Delphi library, <code>Free</code> is the only method I know of that uses this trick.</p> <p>So you don't need to check to see if the variable is <code>Assigned</code> before you call <code>Free</code>; it already does that for you. That's actually why the recommendation is to call <code>Free</code> rather than calling <code>Destroy</code> directly: if you called Destroy on a <code>nil</code> reference, you would get an access violation.</p>

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