iOS Singleton

MySingleton.h

#import <Foundation/Foundation.h>

@interface MySingleton : NSObject

- (id)sharedInstance;

@end

MySingleton.m

#import "MySingleton.h"

@implementation MySingleton

- (id)sharedInstance
{
    static dispatch_once_t pred;
    __strong static MySingleton *shared = nil;
    
    dispatch_once(&pred, ^{
        shared = [[MySingleton alloc] init];
    });
    return shared;
}

@end

Code snippet for creating a singleton using GCD in iOS.