objc的单例问题
最近我读别人的代码，看到他写的单例模式修改了retain, release:

C/C++ code

- (id)retain{        return self;    }- (unsigned)retainCount{    return UINT_MAX;  //denotes an object that cannot be released}- (oneway void)release{    //do nothing}- (id)autorelease{    return self;    }- (void)dealloc {    [_sharedManager release];    [super dealloc];}

请问这样做是否必要呢？另外，如何让这个类只能调用shardInstance，而不让别人调用alloc init呢？

[解决办法]

C/C++ code

+(AppropriateSingleton *) sharedAppropriateSingleton {    @synchronized (self) {        if (instance_ == nil) {//            instance_ = [[super allocWithZone:NULL] init]; // OR            instance_ = [NSAllocateObject([self class], 0, NULL) init];        }    }        return instance_;}+(id) allocWithZone:(NSZone *)zone {    @synchronized (self) {        return [[self sharedAppropriateSingleton] retain];    }}-(id) copyWithZone:(NSZone *) zone {    return self;}