8.2.1. What You Can and Cannot Do in +load
8.2.1 What You Can and Cannot Do in +load
+load 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
+load is executed; hence
+load works best for executing C code that is independent on the Objective-C runtime.
+load implementation in the GNU runtime guarantees you the following things:
- you can write whatever C code you like;
- you can allocate and send messages to objects whose class is implemented in the same file;
+loadimplementation of all super classes of a class are executed before the
+loadof that class is executed;
+loadimplementation of a class is executed before the
+loadimplementation of any category.
In particular, the following things, even if they can work in a particular case, are not guaranteed:
- allocation of or sending messages to arbitrary objects;
- allocation of or sending messages to objects whose classes have a category implemented in the same file;
- sending messages to Objective-C constant strings (
@"this is a constant string");
You should make no assumptions about receiving
+load in sibling classes when you write
+load of a class. The order in which sibling classes receive
+load is not guaranteed.
The order in which
+initialize are called could be problematic if this matters. If you don’t allocate objects inside
+load, it is guaranteed that
+load is called before
+initialize. If you create an object inside
+initialize method of object’s class is invoked even if
+load was not invoked. Note if you explicitly call
+load on a class,
+initialize will be called first. To avoid possible problems try to implement only one of these methods.
+load 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
+load 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.
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Licensed under the GNU Free Documentation License, Version 1.3.