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What’s the difference between Any and AnyObject?

Written by Paul Hudson    @twostraws

Swift has two anonymous types: Any and AnyObject. They are subtly different, and you will need to use both sooner or later.

AnyObject refers to any instance of a class, and is equivalent to id in Objective-C. It’s useful when you specifically want to work with a reference type, because it won’t allow any of Swift’s structs or enums to be used. AnyObject is also used when you want to restrict a protocol so that it can be used only with classes.

Any refers to any instance of a class, struct, or enum – literally anything at all. You’ll see this in Swift wherever types are unknown or are mixed in ways that can be meaningfully categorized:

let values: [Any] = [1, 2, "Fish"]

Ideally you should avoid both Any and AnyObject in your code – it’s better to be more specific if you can be.

Available from iOS 8.0 – learn more in my book Swift Design Patterns

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