[swift-evolution] Will Swift ever support optional methods without @objc?

[Shawn Erickson]

This has been discussed somewhat heavily in the past and nothing yet has
really moved forward on it. I do think a good way of doing something like
this would be helpful. I have resulted to defining an interface with an
extension that provides empty defaults and for each function a match bool
var exists to imply if it exists or not. The code accepting a delegate can
probe these bool vars to configure itself to efficiently operate based on
knowledge about what the delegate expects (some missing from most proposed
solutions other then @objc optional).
On Tue, Nov 15, 2016 at 6:59 AM Karl via swift-evolution <
swift-evolution at swift.org> wrote:

>
> On 15 Nov 2016, at 12:22, Haravikk via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>
> On 15 Nov 2016, at 07:53, Rick Mann via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>
> On Nov 14, 2016, at 22:51 , Charlie Monroe via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> One major example is the NS/UITableViewDataSource or Delegate - there are
> many many methods that you don't need to implement, hence are optional.
>
> But I think that this was partially solved by default implementation of
> protocol methods, which pretty much does what you want...
>
>
> I just realized I only responded to someone else, and not the whole list.
> It does, but it forces me to make the return value of the protocol method
> optional, so that the default implementation can return nil.
>
> In the end, I guess that's not so bad, since I'm not happy with the entire
> approach, but it'll do for now.
>
>
> What's different about having the method return nil vs being optional?
> You're attempting to call it either way, and presumably need some means of
> handling the return value, except in Swift it's all nice and explicit and
> easy to put in a conditional like:
>
> if let result = myObject.someOptionalMethod() { /* Do some stuff */ }
> print(myObject.someOptionalStringMethod() ?? "")
>
> And so-on. If you need a method to be both optional, and return a nilable
> result then you can use a double optional like so:
>
> if let result = myObject.someDoubleOptionalMethod() { // Method was
> implemented
> if let value = result { // Method returned a value
> /* Do some stuff */
> }
> }
>
>
> By defining the methods as returning an Optional and throwing in default
> implementations you can specify fewer, bigger protocols and make clear what
> the requirements really are, though personally given the choice I'd prefer
> a dozen smaller protocols that are absolutely explicit in what they do.
>
> But yeah, I think the tools you need are all there already; maybe there's
> an argument to be made for allowing default return values on protocol
> methods, to reduce the boiler-plate?
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>
>
> I think there is a difference between:
>
> - A method which returns an optional result, and
> - An optional method which, if present, always returns a result
>
> Perhaps not so much of a difference at the usage site (it’s just a
> question of placing a ? for optional chaining), but semantically and when
> conforming to the protocol, they mean different things.
>
> - Karl
>
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