Singleton pattern

SingletonClass.h

#import <Foundation/Foundation.h>

@interface SingletonClass : NSObject

+ (SingletonClass *) sharedInstance;

@end

SingletonClass.m

#import "SingletonClass.h"

static SingletonClass * sharedInstance = nil;


@interface SingletonClass ()

- (id) initPrivately; // We don't override init, which can be called externally

@end


@implementation SingletonClass

+ (SingletonClass *) sharedInstance {
    static dispatch_once_t onceToken;
        dispatch_once(&onceToken, ^{
            sharedInstance = [[super allocWithZone:nil] initPrivately];
        });
    return sharedInstance;
}

- (id)initPrivately {
    if (!(self = [super init]))
        return nil;
    return self;
}

- (void)dealloc {
    [super dealloc];
}

#pragma mark - Singleton

// Methods that assist this class in acting as a singleton
+ (id)allocWithZone:(NSZone*)zone { return sharedInstance; }
- (id)copyWithZone:(NSZone *)zone { return self; }
- (id)retain { return self; }
- (NSUInteger)retainCount { return UINT_MAX; }
- (void)release {}
- (id)autorelease { return self; }

@end