Why is an Array an AnyObject in Swift?

Question

I'm having trouble understanding the limitations of AnyObject.

You can see from the header that Array is a struct. Nevertheless, this code works:

var whatobject : AnyObject
whatobject = [1,2]

And it's not just literal arrays:

var whatobject : AnyObject
let arr = [1,2,3]
whatobject = arr

However, I can't assign a struct that I make to whatobject:

struct S {}
var whatobject : AnyObject
whatobject = S() // error

So an array isn't really a struct after all?

Bryan Chen · Accepted Answer · 2014-06-11 04:43:43Z

8

that's the fun part when bridging comes in...

by default, Swift bridge

Int (and friends) to NSNumber
String to NSString
Dictionary to NSDictionary

so compiler will change them to object if need to

and you can do

var num : AnyObject = 1 // I think num is now NSNumber
var arr : AnyObject = [1,2,3] // I think arr is now NSArray of @[@1,@2,@3]

and you can't assign sturct/enum to AnyObject because they are not object type (you can use Any to hold them)

edited Jun 11, 2014 at 4:43

answered Jun 11, 2014 at 3:58

Bryan Chen

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10 Comments

matt Over a year ago

Wow, I certainly hadn't thought of it that way before!

Bryan Chen Over a year ago

I hope Apple will change this kind of auto bridge behaviour. It introduced lots hard to find bugs.

matt Over a year ago

Really? Can you give me an example?

Bryan Chen Over a year ago

structs are call by value and objects are call by reference, so you may modify (or not modify even you want to) something because you expect get a reference but get value (or other way around). it won't happen normally, but will cause you trouble when writing generic code. (I already give up to fight with compiler with some generic library code I want to write)

BergQuester Over a year ago

FYI, I get errors complaining about type conversions when I enter your code into a playground.

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