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113 lines
4.7 KiB
HTML
113 lines
4.7 KiB
HTML
4 years ago
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<title>What you can and what you cannot do in +load - Using the GNU Compiler Collection (GCC)</title>
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<link rel="up" href="Executing-code-before-main.html#Executing-code-before-main" title="Executing code before main">
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<body>
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<div class="node">
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<a name="What-you-can-and-what-you-cannot-do-in-+load"></a>
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<a name="What-you-can-and-what-you-cannot-do-in-_002bload"></a>
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<p>
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Up: <a rel="up" accesskey="u" href="Executing-code-before-main.html#Executing-code-before-main">Executing code before main</a>
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<hr>
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</div>
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<h4 class="subsection">8.2.1 What You Can and Cannot Do in <code>+load</code></h4>
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<p><code>+load</code> is to be used only as a last resort. Because it is
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executed very early, most of the Objective-C runtime machinery will
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not be ready when <code>+load</code> is executed; hence <code>+load</code> works
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best for executing C code that is independent on the Objective-C
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runtime.
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<p>The <code>+load</code> implementation in the GNU runtime guarantees you the
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following things:
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<ul>
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<li>you can write whatever C code you like;
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<li>you can allocate and send messages to objects whose class is implemented
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in the same file;
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<li>the <code>+load</code> implementation of all super classes of a class are
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executed before the <code>+load</code> of that class is executed;
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<li>the <code>+load</code> implementation of a class is executed before the
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<code>+load</code> implementation of any category.
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</ul>
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<p>In particular, the following things, even if they can work in a
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particular case, are not guaranteed:
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<ul>
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<li>allocation of or sending messages to arbitrary objects;
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<li>allocation of or sending messages to objects whose classes have a
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category implemented in the same file;
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<li>sending messages to Objective-C constant strings (<code>@"this is a
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constant string"</code>);
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</ul>
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<p>You should make no assumptions about receiving <code>+load</code> in sibling
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classes when you write <code>+load</code> of a class. The order in which
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sibling classes receive <code>+load</code> is not guaranteed.
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<p>The order in which <code>+load</code> and <code>+initialize</code> are called could
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be problematic if this matters. If you don't allocate objects inside
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<code>+load</code>, it is guaranteed that <code>+load</code> is called before
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<code>+initialize</code>. If you create an object inside <code>+load</code> the
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<code>+initialize</code> method of object's class is invoked even if
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<code>+load</code> was not invoked. Note if you explicitly call <code>+load</code>
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on a class, <code>+initialize</code> will be called first. To avoid possible
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problems try to implement only one of these methods.
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<p>The <code>+load</code> method is also invoked when a bundle is dynamically
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loaded into your running program. This happens automatically without any
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intervening operation from you. When you write bundles and you need to
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write <code>+load</code> you can safely create and send messages to objects whose
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classes already exist in the running program. The same restrictions as
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above apply to classes defined in bundle.
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</body></html>
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