initWith vs arrayWith in objC?

Question

What are the pros and cons of creating an array (or any other collection using its respective factory method) with

[[NSArray alloc] init]

vs

[NSArray array]

in objective C? It seems like the latter factory method allows us to not worry about memory management, so I was curious if there's any point in ever using alloc + init, though I'm now more interested in all the differences between these two, and why one would choose one over the other.

Answer 1

Prior to ARC there was a critical difference. The alloc/init case returned a retained object, while the array case returned an autoreleased object.

With ARC the difference is less important. Probably the first case is a hair more efficient, but in most scenarios they are interchangeable.

Answer 2

In the first one, you have the ownership of array object & you have to release them.

NSMutableArray* p = [[NSMutableArray alloc] init];

[p release];

& last one you dont need to release as you don't have the ownership of array object.

NSMutableArray* p = [NSMutableArray]; //this is autoreleased

If you call release in this, then it will crash your application.