Question

According to Cocoa Programming for Mac OS X, 3rd Edition, on page 202 (chapter 13):

You will be registering, reading, and setting defaults in several classes in your application. To make sure that you always use the same name, you should declare those strings in a single file and then simply #import that file into any file in which you use the names. There are several ways to do this. For example, you could use the C preprocessor’s #define command, but most Cocoa programmers use global variables for this purpose.

Is this really the correct best practice? Global variables? That seems insane to me – counter to everything I’ve ever been taught.

Would a better design be a simple Singleton class with these defined? Or is it really the correct best practice to go global? Is there a better pattern than either, given that many people consider Singletons to be globals in a pretty dress?

Answer 1

Global variables or a singleton will accomplish the same thing here. Both can be used to turn ‘key’ names in Cocoa that won’t throw a compiler error if it’s misspelled into a compiler error. That’s the main purpose. Global variables are a bit easier though seeing as it requires less typing.

Instead of doing this:

[myArray setObject:theObject forKey:MyGlobalVariableKeyName]; 

You’d have to do something along the lines of:

[myArray setObject:theObject              forKey:[[MySingletonVariableClass getInstance] myVariableKeyName]; 

Global variables are essentially less typing for the same effect.