"class" as a thing that can be inherited

Hacksaw · 2021-01-15T18:18:55.890Z

In another thread, I saw this construction:

protocol AssetInstance : class {
    var identifier: String { get set }
}

Which, to my astonishment, compiles. I can't seem to find documentation for this use of the keyword "class".

Could I get a pointer, please?

krilnon · 2021-01-15T18:22:23.016Z

It's another name for AnyObject.

This proposal merges the concepts of class and AnyObject , which now have the same meaning: they represent an existential for classes. To get rid of the duplication, we suggest only keeping AnyObject around. To reduce source-breakage to a minimum, class could be redefined as typealias class = AnyObject and give a deprecation warning on class for the first version of Swift this proposal is implemented in. Later, class could be removed in a subsequent version of Swift.

github.com

apple/swift-evolution/blob/main/proposals/0156-subclass-existentials.md#class-and-anyobject

# Class and Subtype existentials

* Proposal: [SE-0156](0156-subclass-existentials.md)
* Authors: [David Hart](http://github.com/hartbit), [Austin Zheng](http://github.com/austinzheng)
* Review Manager: [Doug Gregor](https://github.com/DougGregor)
* Status: **Implemented (Swift 4)**
* Decision Notes: [Rationale](https://forums.swift.org/t/accepted-se-0156-class-and-subtype-existentials/5477)
* Bug: [SR-4296](https://bugs.swift.org/browse/SR-4296)

## Introduction

This proposal brings more expressive power to the type system by allowing Swift to represent existentials of classes and subtypes which conform to protocols.

[Mailing list discussion](https://forums.swift.org/t/subclass-existentials/5024)

## Motivation

Currently, the only existentials which can be represented in Swift are conformances to a set of protocols, using the `&` protocol composition syntax:

```swift

This file has been truncated. show original

Hacksaw · 2021-01-15T18:26:29.916Z

Ah, thanks.

Tino · 2021-01-15T22:46:49.424Z

You are lucky —I tell people all the time to use AnyObject; I guess the old spelling will never fade away

phoneyDev · 2021-01-15T23:20:36.649Z

It's been deprecated, or something.

Class-only protocols, class vs AnyObject? Using Swift

What is the difference, if any, btw P and Q here: protocol P : class { ... } protocol Q : AnyObject { ... } If no difference, which should be preferred? (I got the impression that the class version was meant to be deprecated, but it still compiles without warnings as of Xcode 9.3)

Nevin · 2021-01-16T00:17:49.524Z

Personally, I think class is much clearer in its meaning than AnyObject.

Hacksaw · 2021-01-16T00:32:04.925Z

Not for me. Not in lowercase. It looks like a mistake. If is was Class, mirroring Self, maybe.

AnyObject is fine for me.