Any, AnyObject in Swift

Any and AnyObject

AnyObject is a reserved type in Swift to represent an instance of some class.

It plays a flexible role as a bridge between Objective-C because in Cocoa framework, the id pointer address is core in Cocoa.

However, usage of AnyObject in Swift is pretty cumbersome because AnyObject always represents optional in Swift and we have to extract it’s value as we need like the following. The whole class types in Swift implicitly conform AnyObject protocol includes nothing inherently.

func someMethod() -> AnyObject? {
    // ...

    // result is an `AnyObject?` value, which is equivalent to `id`.
    return result
}

let anyObject: AnyObject? = SomeClass.someMethod()
if let someInstance = anyObject as? SomeRealClass {
    // ...
    // Now, `someInstance` is `SomeRealClass` type. Use it directly.

    someInstance.funcOfSomeRealClass()
}

I figured out the need of Any type is from here. The Any type in Swift is not only covering class instance type but struct or enum type. We could use Any to represent literally any type of swift but optional. You must append suffix ? to Any for covering optional types.

Implicit type conversion to Objective-C

The more interesting was how the swift compiler and Foundation framework convert primitive Swift types into Cocoa types like String -> NSString.

Let me show the following example.

import UIKit

let swiftInt: Int = 1
let swiftString: String = "miao"

var array: [AnyObject] = []
array.append(swiftInt)
array.append(swiftString)

I’d import Foundation implicitly by adding import UIKit makes Swift Array of AnyObject appends Int or String(value type) into AnyObject because Foundation converts Swift primitive value types into Cocoa class types(NSNumber, NSString).

By removing UIKit, the Swift compiler generate error.

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References

ANY AND ANYOBJECT