Objective C static vs. dynamic constructors

Question

Hi,

Is it best to have static constructors where you alloc the instance in the constructor and you return the instance as auto release, e.g. [String stringWithFormat...] or is it best to have dynamic constructors where you ask the user to alloc first so that he is in charge of releasing? When should you use each?

Cheers

Answer 1

First, there is no such thing as a "constructor" in Objective-C. Nor is there "static vs. dynamic constructors". You got the C++ taint and it is hampering your ability to understand Objective-C! :)

You'll want to read (and re-read) the memory management guide.

Notably specific to your question, if you have class method like +stringWithFormat:, then that method should return an autoreleased instance. Generally, it would be implemented like:

+ stringWithFoo: (Foo *) aFoo
{
     return [[[self alloc] initWithFoo: aFoo] autorelease];
}

(Simplified slightly to avoid varargs noise).