[swift-evolution] AnyProtocol proposal

[Developer]

What are the advantages of using AnyProtocol over a simple `class` constraint?  To my mind, If you're already using Any or AnyObject in an interface, it seems comfortable enough with dynamic dispatch that knowing the underlying representation of the thing you've got won't do you much good.  

In your specific class, my thinking is a delegate need not be a protocol only if an Object presents just a good a target for a message.

~Robert Widmann

2016/02/11 9:08、João Nunes via swift-evolution <swift-evolution at swift.org> のメッセージ:

> Hello,
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> I have been thinking about a case that is missing completely from swift.
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> We have the AnyObject type to represent an Object of any type. 
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> I recently run upon a situation where i needed a type to represent any Protocol. A AnyProtocol Type would be useful for my case.
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> Example:
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> I have a generic class that needs to receive a protocol type. The code without the AnyProtocol is the following:
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> public class MulticastDelegate<T> {
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> 	private var delegates = NSHashTable.weakObjectsHashTable()
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> 	
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> 	public init() {}
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> 	public func addDelegate(delegate: T) {
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> 		guard delegate is AnyObject else { return }
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> 		delegates.addObject((delegate as! AnyObject))
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> 	}
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> }
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> This code needs to “trust” that T is a protocol and also make sure T is an Object.
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> Example using AnyProtocol, if it existed:
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> public class MulticastDelegate<T:AnyProtocol> {
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> 	private var delegates = NSHashTable.weakObjectsHashTable()
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> 	
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> 	public init() {}
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> 	public func addDelegate(delegate: T) {
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> 		delegates.addObject(delegate)
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> 	}
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> }
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> Note that the protocol must be a class protocol. This could also be achieved with a where clause or AnyClassProtocol variant.
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> This example is also available on github: https://github.com/jonasman/MulticastDelegate
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> To extend my proposal, there might be cases where AnyStruct and AnyEnum would be usefull. I have no examples for these cases, but i believe someone might have it.
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> What are your thoughts, should I open a PR proposal?
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> João Nunes
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> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
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