An implementation of a Singleton accesAn implementation of a Singleton accessor routine. Removes the (one if-statement) overhead of calling dispatch_once after the first time by method swizzling sharedInstance for a method without dispatch_once

SingletonInitializer.m

#import <dispatch/dispatch.h>
#import <objc/runtime.h>

@implementation MySingleton

static MySingleton * __singleton = nil;

+ (MySingleton *) sharedInstance_accessor
{
	return ( __singleton );
}

+ (MySingleton *) sharedInstance
{
	static dispatch_once_t __once = 0;
	
	dispatch_once( &__once, ^{ 
                __singleton = [[self alloc] init]; 
		Method plainMethod = class_getInstanceMethod( self, @selector(sharedInstance) );
		Method accessorMethod = class_getInstanceMethod( self, @selector(sharedInstance_accessor) );
		method_exchangeImplementations( plainMethod, accessorMethod );
        });
	return ( __singleton );
}

@end

Should it be class_getInstanceMethod or class_getClassMethod?