ObjC Singleton Class Template

FooClass.h

@interface FooClass : NSObject
+ (FooClass *)sharedInstance;
@end

FooClass.m

@implementation FooClass

+ (FooClass *)sharedInstance
{
  static dispatch_once_t onceToken;
  static FooClass *sharedInstance = nil;
    
  dispatch_once(&onceToken, ^{
    sharedInstance = [[FooClass alloc] init];
  });
    
  return sharedInstance;
}

@end