[swift-users] Can't make an escaping closure argument optional?

[Shawn Erickson]

At the moment an optional closure is considered escaping so you don’t have
to state it using @escaping and as you see you actually can’t. A bug or two
exists against Swift related this and I don’t know their current state.

If after removing @escaping things still fail to compile please post a code
example.

-Shawn
On Fri, Jan 5, 2018 at 1:17 PM Kenny Leung via swift-users <
swift-users at swift.org> wrote:

> Because it’s being assigned to an ivar, it’s forced to be escaping, or so
> the compiler tells me.
>
> -Kenny
>
>
> On Jan 5, 2018, at 12:04 PM, Kevin Nattinger <swift at nattinger.net> wrote:
>
> If you remove the @escaping you'll notice it doesn't complain about a
> non-escaping closure escaping.
> I could be wrong, but I believe that's because using it as an associated
> value forces it to escape on the calling side.
>
> func esc(_ x: @escaping () -> ()) {
>     x()
> }
> func noesc(_ x: () -> ()) {
>     x()
> }
>
> func foo() {
>     noesc {
>         print(owner) // compiles
>     }
>     esc {
>         print(owner) // error: requires explicit 'self.'…
>     }
>     Optional<()->()>.some {
>         print(owner) // error: requires explicit 'self.'…
>     }
> }
>
>
> On Jan 5, 2018, at 11:48 AM, Kenny Leung via swift-users <
> swift-users at swift.org> wrote:
>
> Hi All.
>
> It seems that if you have an escaping closure argument, you can’t make it
> optional. Am I right?
>     init (
>         owner:AnyObject,
>         handler:@escaping (HXObserverNotification)->Void
>         ) {
>         self.owner = owner
>         self.handler = handler
>     }
>
> You could try this:
>     init (
>         owner:AnyObject,
>         handler:@escaping ((HXObserverNotification)->Void)?
>         ) {
>         self.owner = owner
>         self.handler = handler
>     }
> You get “@escaping attribute only applies to function types”
>
> Or you could try this:
>     init (
>         owner:AnyObject,
>         handler:(@escaping (HXObserverNotification)->Void)?
>         ) {
>         self.owner = owner
>         self.handler = handler
>     }
> You get “@escaping attribute may only be used in function parameter
> position”
>
> -Kenny
>
>
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