Is an empty array created using alloc and init automatically set to nil?

Question

Just a simple question, I hope.

When creating an array using alloc and init, i.e. without specifying 'initWith...' or preloading it with objects, is that array automatically set to nil?

For example:

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

And would the same apply when you use the class method array?

NSMutableArray *buffetItems = [NSMutableArray array];

I was having trouble visualising how exactly 'empty' is represented. Count = zero seems to be it. — cheznead
– cheznead, Commented Feb 4, 2015 at 23:09
You can have a shelf with all your books on it; you can have a shelf which doesn't contain any books; you can have a wall with no shelf. You can have an array that has strings in it; you can have an array which doesn't contain any objects; you can have an array variable with no array. — jscs
– jscs, Commented Feb 4, 2015 at 23:23
'array variable with no array': awesome way of encapsulating it. Thanks a ton Josh! P.S I like the carrick bend ;) — cheznead
– cheznead, Commented Feb 4, 2015 at 23:35

Linuxios · Accepted Answer · 2015-02-04 22:21:20Z

1

No.

nil and the empty array are completely different things in Objective-C, unlike, say Lisp.

nil is (for all intents and purposes) an opaque value that indicates the absence of any value in a variable. This is fundamentally semantically different than the absence of elements in an array.

answered Feb 4, 2015 at 22:21

Linuxios

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11 Comments

cheznead Over a year ago

So when you create an array with alloc and init, what value is it initialised to? Or is it simply allocated a memory address?

Linuxios Over a year ago

@shinnyWhack: the empty array.

Linuxios Over a year ago

@shinnyWhack: the array with no elements in. It.

cheznead Over a year ago

How is that represented? By 0?

Linuxios Over a year ago

Yes, and no. It has a value - that value is the empty array. Think of it this way: nil is having nothing, and the empty array is having an empty box. You still have something, it just doesn't have anything in it.

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