What kind of object does @[obj1, obj2] create?

Question

I came across the following:

NSArray *array = @[object1, object2];

It seems to be creating an NSArray, but is this array instance an autoreleased object, or must I release it?

Hagar

Answer 1

This is a new collection literal available in the compiler that ship with xcode 4.4 and above

@[object1, object2];

is equivalent to

[NSArray arrayWithObjects:object1, object2, nil];

so yes, it is an autoreleased object, if you need this to be retained, you can do

myRetainedArray = [@[object1, object2] retain];

this question has a good description of all of the new literals

Actaeon

if I need to create a not autorelease object, can't use above literal? – Hagar

you can still use it, just retain the array afterwards – Actaeon

Thanks wattson12. Is it also possible to intentionally release above autoreleased object? – Hagar

this literal is just a convenience to make creating arrays neater. you still have to manage its memory the same as you would with any other object (or switch to ARC) – Actaeon

"is equivalent to" It's not equivalent. It uses arrayWithObjects:count: internally. arrayWithObjects: will stop at the first nil argument, which means if you have a nil value in the list, it will stop there, and there is no error; whereas with array literals (as well as arrayWithObjects:count:), it will throw an exception if one of the things in the list is nil. – Ballyrag

Answer 2

It's the new llvm compiler's literal for creating an array. The compiler changes this to:

NSArray *array = [NSArray arrayWithObjects: object1,object2,nil];

So it is returning an autoreleased object.

A Google search brought up further info:

http://clang.llvm.org/docs/ObjectiveCLiterals.html

Radiobiology

"The compiler changes this to:" No, it changes it to use arrayWithObjects:count:. – Ballyrag