1<html lang="en"> 2<head> 3<title>What you can and what you cannot do in +load - Using the GNU Compiler Collection (GCC)</title> 4<meta http-equiv="Content-Type" content="text/html"> 5<meta name="description" content="Using the GNU Compiler Collection (GCC)"> 6<meta name="generator" content="makeinfo 4.13"> 7<link title="Top" rel="start" href="index.html#Top"> 8<link rel="up" href="Executing-code-before-main.html#Executing-code-before-main" title="Executing code before main"> 9<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> 10<!-- 11Copyright (C) 1988-2013 Free Software Foundation, Inc. 12 13Permission is granted to copy, distribute and/or modify this document 14under the terms of the GNU Free Documentation License, Version 1.3 or 15any later version published by the Free Software Foundation; with the 16Invariant Sections being ``Funding Free Software'', the Front-Cover 17Texts being (a) (see below), and with the Back-Cover Texts being (b) 18(see below). 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Because it is 56executed very early, most of the Objective-C runtime machinery will 57not be ready when <code>+load</code> is executed; hence <code>+load</code> works 58best for executing C code that is independent on the Objective-C 59runtime. 60 61 <p>The <code>+load</code> implementation in the GNU runtime guarantees you the 62following things: 63 64 <ul> 65<li>you can write whatever C code you like; 66 67 <li>you can allocate and send messages to objects whose class is implemented 68in the same file; 69 70 <li>the <code>+load</code> implementation of all super classes of a class are 71executed before the <code>+load</code> of that class is executed; 72 73 <li>the <code>+load</code> implementation of a class is executed before the 74<code>+load</code> implementation of any category. 75 76 </ul> 77 78 <p>In particular, the following things, even if they can work in a 79particular case, are not guaranteed: 80 81 <ul> 82<li>allocation of or sending messages to arbitrary objects; 83 84 <li>allocation of or sending messages to objects whose classes have a 85category implemented in the same file; 86 87 <li>sending messages to Objective-C constant strings (<code>@"this is a 88constant string"</code>); 89 90 </ul> 91 92 <p>You should make no assumptions about receiving <code>+load</code> in sibling 93classes when you write <code>+load</code> of a class. The order in which 94sibling classes receive <code>+load</code> is not guaranteed. 95 96 <p>The order in which <code>+load</code> and <code>+initialize</code> are called could 97be problematic if this matters. If you don't allocate objects inside 98<code>+load</code>, it is guaranteed that <code>+load</code> is called before 99<code>+initialize</code>. If you create an object inside <code>+load</code> the 100<code>+initialize</code> method of object's class is invoked even if 101<code>+load</code> was not invoked. Note if you explicitly call <code>+load</code> 102on a class, <code>+initialize</code> will be called first. To avoid possible 103problems try to implement only one of these methods. 104 105 <p>The <code>+load</code> method is also invoked when a bundle is dynamically 106loaded into your running program. This happens automatically without any 107intervening operation from you. When you write bundles and you need to 108write <code>+load</code> you can safely create and send messages to objects whose 109classes already exist in the running program. The same restrictions as 110above apply to classes defined in bundle. 111 112 </body></html> 113 114