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Why can I have an [AnyObject] array and put a bunch of different sized types in it ...

var a = [AnyObject]()
a.append(Int(1))
a.append(Float64(3.14))
a.append(Bool(true))

... except for Int32 and Int64 ....

a.append(Int32(1)) // err: type 'Int32' does not conform to protocol 'AnyObject'
a.append(Int64(1)) // err: type 'Int64' does not conform to protocol 'AnyObject'

The documentation for AnyObject says:

“AnyObject can represent an instance of any class type”

But when I command-click on Int, Int32 or Int64 to see the standard library definition of these types, I see that they are all struct values.

What is the underlying issue here? Why is this designed like this?

Stefan Arentz
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3 Answers3

24

There are two kinds of anything types in Swift – Any, which can truly hold anything – a struct, enum or class, and AnyObject, which can only hold classes.

The reason why it seems like AnyObject can hold structs sometimes is that some specific types are implicitly converted to their NSEquivalent for you as needed, to make Objective-C interop less painful.

When you write let ao: AnyObject = Int(1), it isn’t really putting an Int into an AnyObject. Instead, it’s implicitly converting your Int into an NSNumber, which is a class, and then putting that in.

But only some types have this implicit conversion. Int does, but Int32 doesn’t, hence this behaviour:

// fine
let aoInt: AnyObject = Int(1) as NSNumber
// also fine: implicit conversion
let aoImplicitInt: AnyObject = Int(1)
// not fine: error: 'Int32' is not convertible to 'NSNumber'
let aoInt32: AnyObject = Int32(1) as NSNumber
// but the implicit error is less, ahem, explicit
// error: type 'Int32' does not conform to protocol 'AnyObject'
let aoImplicitInt32: AnyObject = Int32(1)

It could be argued there should be more implicit conversions to grease the wheels, but then again, these implicit conversions are the source of much confusion already and the direction in the latest beta is to have fewer of them rather than more.

Airspeed Velocity
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  • Thank you this is an excellent answer. Do you know if there is any documentation about what kind of implicit conversions Swift does? I assume this goes beyond just `NSInteger`. – Stefan Arentz Mar 07 '15 at 21:54
  • Yup, it’s covered in the [Using Swift with Cocoa and Objective-C](https://developer.apple.com/library/ios/documentation/Swift/Conceptual/BuildingCocoaApps/WorkingWithCocoaDataTypes.html#//apple_ref/doc/uid/TP40014216-CH6-XID_42) iBook. But just be aware that it’s changed in the Xcode 6.3 beta and the book only reflects the release version behaviour, so best to check the Xcode release notes when you try upgrading. – Airspeed Velocity Mar 07 '15 at 21:59
  • BTW You mean NSNumber and not NSInteger I assume? – Stefan Arentz Mar 07 '15 at 22:11
0

The protocol that gives Int et al this ability is _ObjectiveCBridgeable, which you can adopt yourself if you feel adventurous.

Community
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user2488730
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0

Because Int is a value Type.

AnyObject refers to referance types (classes) not value types

Any refers to referance types + value types (structs + classes)

You must use Any for valueTypes, not AnyObject

Value Types > generally structs, enums, bla bla..

Referance Types > generally classes

There are two types of variables > Referance types and value types

Referance types are pointer types and generally contains a ram address value where the original data is stored

Value types are not addresses . They directly contain the variable value

Int asd = 3 (asd directly contains 3)

Int, Float, number types,... Date are almost always struct(value type) in most computer languages.

String is almost always a hybrid in most computer languages

ViewControllers, Views, Buttons, ...arrays, dictionaries, ... and your custom defined classes are referance types

Add080bbA
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