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<title>Using the GNU Compiler Collection (GCC): What you can and what you cannot do in +load</title>

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Up: <a href="Executing-code-before-main.html#Executing-code-before-main" accesskey="u" rel="up">Executing code before main</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<a name="What-You-Can-and-Cannot-Do-in-_002bload"></a>
<h4 class="subsection">8.2.1 What You Can and Cannot Do in <code>+load</code></h4>

<p><code>+load</code> is to be used only as a last resort.  Because it is
executed very early, most of the Objective-C runtime machinery will
not be ready when <code>+load</code> is executed; hence <code>+load</code> works
best for executing C code that is independent on the Objective-C
runtime.
</p>
<p>The <code>+load</code> implementation in the GNU runtime guarantees you the
following things:
</p>
<ul>
<li> you can write whatever C code you like;

</li><li> you can allocate and send messages to objects whose class is implemented
in the same file;

</li><li> the <code>+load</code> implementation of all super classes of a class are
executed before the <code>+load</code> of that class is executed;

</li><li> the <code>+load</code> implementation of a class is executed before the
<code>+load</code> implementation of any category.

</li></ul>

<p>In particular, the following things, even if they can work in a
particular case, are not guaranteed:
</p>
<ul>
<li> allocation of or sending messages to arbitrary objects;

</li><li> allocation of or sending messages to objects whose classes have a
category implemented in the same file;

</li><li> sending messages to Objective-C constant strings (<code>@&quot;this is a
constant string&quot;</code>);

</li></ul>

<p>You should make no assumptions about receiving <code>+load</code> in sibling
classes when you write <code>+load</code> of a class.  The order in which
sibling classes receive <code>+load</code> is not guaranteed.
</p>
<p>The order in which <code>+load</code> and <code>+initialize</code> are called could
be problematic if this matters.  If you don&rsquo;t allocate objects inside
<code>+load</code>, it is guaranteed that <code>+load</code> is called before
<code>+initialize</code>.  If you create an object inside <code>+load</code> the
<code>+initialize</code> method of object&rsquo;s class is invoked even if
<code>+load</code> was not invoked.  Note if you explicitly call <code>+load</code>
on a class, <code>+initialize</code> will be called first.  To avoid possible
problems try to implement only one of these methods.
</p>
<p>The <code>+load</code> method is also invoked when a bundle is dynamically
loaded into your running program.  This happens automatically without any
intervening operation from you.  When you write bundles and you need to
write <code>+load</code> you can safely create and send messages to objects whose
classes already exist in the running program.  The same restrictions as
above apply to classes defined in bundle.
</p>


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