Compile date as NSDate

gistfile1.m

+ (NSDate *)compileDate
{
	BOOL (^stringContainsQuestionMark)(NSString *) = ^BOOL (NSString *string) {
		return [string rangeOfString:@"?"].location != NSNotFound;
	};
	
	NSMutableString *dateString = @(__DATE__).mutableCopy;
	NSString *timeString = @(__TIME__);
	if (stringContainsQuestionMark(dateString) || stringContainsQuestionMark(timeString)) {
		return nil;
	}
	[dateString appendFormat:@" %@", timeString];
	
	static NSDateFormatter *compileDateFormatter = nil;
	static NSDate *sentinel = nil;
	static dispatch_once_t onceToken;
	dispatch_once(&onceToken, ^{
		compileDateFormatter = [[NSDateFormatter alloc] init];
		compileDateFormatter.locale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"];
		compileDateFormatter.timeZone = [NSTimeZone timeZoneWithAbbreviation:@"GMT"];
		compileDateFormatter.dateFormat = @"MMM d yyyy HH:mm:ss";
		
		sentinel = [NSDate dateWithString:@"2013-01-01 12:00:00 +0000"];
	});
	
	NSDate *date = [compileDateFormatter dateFromString:dateString];
	
	// Check to make sure that the date isn't something messed up that precedes
	// the sentinel date set at the start of 2013.
	return ([date compare:sentinel] == NSOrderedAscending) ? nil : date;
}