Objective-C and Class Cluster pattern
design-patterns, ios, objective-c
Solution
Basically, the instance you have allocated could be thrown away and replaced with a different instance. Technically, this isn't specific to class clusters and that is why when you call `super` in any `init` method you need to set the result as `self`:
self = [super init];
Problem
I have read some information about Class Cluster pattern, and understood next: public cluster class only provides interface without actual implementation, other classes implement it for different cases; it has some similarities with Abstract Factory pattern: when we call method `+classNameWith...` it depending on arguments can choose the most appropriate subclass and return it. For example, `+[NSNumber numberWithDouble:1.0]`, will return implementation for storing double values. But what i didn't understand: how works `-init...` methods of public cluster class: `[[NSNumber alloc] initWithDouble:1.0]`, as after calling `alloc` it already allocates instance of `NSNumber`, not it's subclass. So, can somebody explain how actually works `alloc-init` methods of public cluster class, and when concrete subclass instantiated and returned?