iOS - Handy way to run a code block once, based on dispatch_once()

NSUserDefaults+Extension.h

#import <Foundation/Foundation.h>

@interface NSUserDefaults (Extension)

/*!
 *  Associates a block of code with a token. If the token has not been used the code block will run immediately.
 *
 *  @param token A token unique to the code block
 *  @param block A block of code to run
 *
 *  @return TRUE if the code block was run
 */
bool run_once(NSString *token, dispatch_block_t block);

/*!
 *  Resets a token. The code block associated with it will be run again next time run_once is called
 *
 *  @param token The spent token
 */
+ (void)resetToken:(NSString *)token;

/*!
 *  Checks if a code block with given token will be run. This does not spend the token
 *
 *  @param token The token
 *
 *  @return TRUE if the token is not spent
 */
+ (BOOL)willRunWithToken:(NSString *)token;

@end

NSUserDefaults+Extension.m

#import "NSUserDefaults+Extension.h"

@implementation NSUserDefaults (Extension)

bool run_once(NSString *token, dispatch_block_t block)
{
    if (!token)
    {
        return FALSE;
    }
    
    NSString *identifier = [NSString stringWithFormat:@"defaults.run_once.%@", token];
    
    if (![[NSUserDefaults standardUserDefaults] boolForKey:identifier])
    {
        [[NSUserDefaults standardUserDefaults] setBool:TRUE forKey:identifier];
        [[NSUserDefaults standardUserDefaults] synchronize];
        
		block();
        
        return TRUE;
    }
    
    return FALSE;
}

+ (void)resetToken:(NSString *)token
{
    NSString *identifier = [NSString stringWithFormat:@"defaults.run_once.%@", token];
    [[NSUserDefaults standardUserDefaults] removeObjectForKey:identifier];
    [[NSUserDefaults standardUserDefaults] synchronize];
}

+ (BOOL)willRunWithToken:(NSString *)token
{
    if (!token)
    {
        return FALSE;
    }
    
    NSString *identifier = [NSString stringWithFormat:@"defaults.run_once.%@", token];
    return ![[NSUserDefaults standardUserDefaults] boolForKey:identifier];
}

@end