What you can and what you cannot do in +load - Using the GNU Compiler Collection (GCC)
Description: Using the GNU Compiler Collection (GCC)

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#### 8.2.1 What you can and what you 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.

The `+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;
- the `+load` implementation of all super classes of a class are executed before the `+load` of that class is executed;
- the `+load` implementation of a class is executed before the `+load` implementation 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 `+load` and `+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 `+load` the `+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.

The `+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.