GCD Shared Instance

SharedObject.h

#import <Foundation/Foundation.h>

@interface SharedObject : NSObject

+ (SharedObject *) sharedInstance;

@end

SharedObject.m

#import "SharedObject.h"

@implementation SharedObject

+ (SharedObject *) sharedInstance {
    static dispatch_once_t pred = 0;
    __strong static id _sharedObject = nil;
    dispatch_once(&pred, ^{
        _sharedObject = [[self alloc] init];
    });
    return _sharedObject;
}

@end