Struct Constants Example

Constants.h

FOUNDATION_EXPORT const struct DNSUserDefaults {
    __unsafe_unretained NSString *hasRunBefore;
    __unsafe_unretained NSString *hasMadeInAppPurchase;
} DNSUserDefaults;

Constants.m

#import Constants.h

const struct DNSUserDefaults DNSUserDefaults = {
    .hasRunBefore = @"kHasRunBefore",
    .hasMadeInAppPurchase = @"kDidGiveMeMonies",
};

Usage.m

#import Constants.h

//In a method.
BOOL firstRun = ![[NSUserDefaults standardUserDefaults] boolForKey:DNSUserDefaults.hasRunBefore];
BOOL areWeFriends = [[NSUserDefaults standardUserDefaults] boolForKey:DNSUserDefaults.hasMadeInAppPurchase];