Standard singleton implementation

static MySingleton *sharedInstance = nil;
+ (void)initialize
{
if (sharedInstance == nil)
sharedInstance = [[self alloc] init];
}
+ (id)sharedMySingleton
{
//Already set by +initialize.
return sharedInstance;
}
+ (id)allocWithZone:(NSZone*)zone
{
//Usually already set by +initialize.
@synchronized(self) {
if (sharedInstance) {
//The caller expects to receive a new object, so implicitly retain it
//to balance out the eventual release message.
return [sharedInstance retain];
} else {
//When not already set, +initialize is our caller.
//It's creating the shared instance, let this go through.
return [super allocWithZone:zone];
}
}
}
- (id)init
{
//If sharedInstance is nil, +initialize is our caller, so initialize the instance.
//If it is not nil, simply return the instance without re-initializing it.
if (sharedInstance == nil) {
self = [super init];
if (self) {
//Initialize the instance here.
}
}
return self;
}
- (id)copyWithZone:(NSZone*)zone
{
return self;
}
- (id)retain
{
return self;
}
- (unsigned)retainCount
{
return UINT_MAX; // denotes an object that cannot be released
}
- (void)release
{
// do nothing
}
- (id)autorelease
{
return self;
}