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

[Kenny Leung]

You are correct! Thanks!

-Kenny


> On Jan 5, 2018, at 1:24 PM, Shawn Erickson <shawnce at gmail.com> wrote:
> 
> 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 <mailto: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 <mailto: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 <mailto: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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>> 
> 
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