[swift-evolution] [Idea] How to eliminate 'optional' protocol requirements

[Douglas Gregor]

> On Apr 15, 2016, at 5:24 PM, Brent Royal-Gordon <brent at architechies.com> wrote:
> 
>> That’s the other part of my argument: if it is true that Swift code only needs to conform to ObjC protocols with optional requirements, but Swift code does not need to invoke optional requirements of ObjC protocols except very rarely, then it’s okay for calling-an-optional-requirement not to be part of the Swift language.
> 
> How much of a complication is the `methodName?` behavior?

It’s a semi-complicated path through the type checker, but it’s not awful to maintain. There’s a bit of a “fix it or remove it” issue here, because it doesn’t work for settable properties, even though there are very few such things. 

> If you're confident that `optional` is the wrong choice for protocols designed in the future, perhaps you could just make it impossible to declare a new optional requirement in Swift, but leave the calling behavior as-is?

Sure, we can make it arbitrarily hard to use. For example, calling it @objc_optional or similar would reinforce that it’s an Objective-C compatibility feature rather than an intended Swift feature.

	- Doug