#import "SomeClass.h"

static SomeClass *instance = nil;

@implementation SomeClass

#pragma mark -
#pragma mark Singleton

+ (id)instance
{
	@synchronized(self)
	{
		if (instance == nil)
			instance = [[super allocWithZone:NULL] init];
	}
	return instance;
}

+ (id)allocWithZone:(NSZone *)zone
{
	return [[self instance] retain];
}

- (id)copyWithZone:(NSZone *)zone 
{
    return self;
}

- (id)retain 
{
    return self;
}

- (unsigned)retainCount {
    return UINT_MAX; 
}

- (void)release 
{
    // never release
}

- (id)autorelease 
{
    return self;
}

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

@end

Singleton Class

Objective C