NSNumber constants in Obj-C

objective-c ios constants nsnumber
DrWurm picture DrWurm · Sep 4, 2012 · Viewed 11.3k times · Source

I want to make some NSNumber constants via the same style used for NSStrings in this topic. That is, I'm creating separate constants.h/.m files and importing them into classes that need to access them.

Answer

Chuck picture Chuck · Sep 4, 2012

The trouble with doing this is that there isn't such a thing as a compile-time constant NSNumber. Only NSString gets that distinction. NSNumbers are always created dynamically. You can fake it by using a function that runs at your program's startup to initialize the variables. Your options:

  1. Create a class with a +load method that performs the initialization.

  2. In the file with the constants, include a function with __attribute__((constructor)). So, for example:

    // Constants.m

NSNumber *someGlobalNumber;

__attribute__((constructor))
static void InitGlobalNumber() {
    someGlobalNumber = [[NSNumber numberWithInteger:1] retain];
}

But of course then you can't reliably use these numbers in any other functions which are run that early in the startup process. This usually isn't a problem, but is worth keeping in mind.

The other option, which I've seen crop up a few times, is to have a class with accessors for the numbers instead of giving raw access to the variables. It's a bit of a heavier design, but it also feels less voodooish, which has its charms.

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