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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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| <a name="What-you-can-and-what-you-cannot-do-in-_002bload"></a> |
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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> [<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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| <h4 class="subsection">8.2.1 What you can and what you 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>@"this is a |
| constant string"</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’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’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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| Up: <a href="Executing-code-before-main.html#Executing-code-before-main" accesskey="u" rel="up">Executing code before main</a> [<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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