Cocoa Singleton implementation [MRC]

ACSingleton.m

#import "ACSingleton.h"
@implementation ACSingleton

#pragma mark -
#pragma mark Singelton Pattern

static ACSingleton.h* _sharedInstance;

// Method to get the shared instance
+ (id)sharedInstance
{
    if (_sharedInstance == nil) {
        _sharedInstance = [[super allocWithZone:NULL] init];
    }
    return _sharedInstance;
}


// Strict singelton implementation, 
// sharedInstance method is also called when using an allocation method
+ (id)allocWithZone:(NSZone *)zone
{
    return [[self sharedInstance] retain];
}


// No copies are allowed
- (id)copyWithZone:(NSZone *)zone
{
    return self;
}


// Object will never be released
- (void)release
{
    //do nothing
}


// No multiple retains
- (id)retain
{
    return self;
}


// Autorelease does nothing
- (id)autorelease
{
    return self;
}


// Retain count is never zero
- (NSUInteger)retainCount
{
    return NSUIntegerMax;  //denotes an object that cannot be released
}



#pragma mark -
#pragma mark Initialization

// Init methode to override by subclass
- (id)init 
{
    // Prevent class from being initialized multiple times
    if (_sharedInstance) return _sharedInstance;

    self = [super init];
    if (self) {
        // Initialize iVars
    }
    return self;
}


@end