[swift-users] @escaping may only be applied to parameters of function type

[Rick Mann]

But the Apple declaration (accessible via Xcode) of the method it's based on looks like this:

open func enumerator(at url: URL,
    includingPropertiesForKeys keys: [URLResourceKey]?,
    options mask: FileManager.DirectoryEnumerationOptions = [],
    errorHandler handler: (@escaping (URL, Error) -> Bool)? = nil)
        -> FileManager.DirectoryEnumerator?

handler is optional, but has @escaping. Is this an artifact of how Xcode presents system header files?


> On Sep 13, 2016, at 20:11 , Michael Ilseman <milseman at apple.com> wrote:
> 
> TL;DR: The optional is already escaping, due to the fact that “T?" is sugar for Optional<T>, and the noescape-by-default rule only applies to types in immediate parameter position. Current Swift master has much better diagnostics for this case.
> 
> There is not currently a general solution involving escapability of closure types used a generic parameters or tuple members, though such a thing would be useful in Swift 4.
> 
>> On Sep 13, 2016, at 7:42 PM, Shawn Erickson via swift-users <swift-users at swift.org> wrote:
>> 
>> The following is the earlier thread I was talking about. 
>> 
>> [swift-users] Swift 3 (Xcode 8 GM) issue with @escaping 
>> 
>> -Shawn
>> 
>> On Tue, Sep 13, 2016 at 7:31 PM Shawn Erickson <shawnce at gmail.com> wrote:
>> I hit this issue as well. I had an early email on this list regarding do this topic, not in a situation to search for it. It is a short coming in how escaping can be applied to things like optional closures.
>> 
>> I was in the process of authoring an email for swift evolution about it and haven't yet gotten around to filing a defect about it.
>> 
>> -Shawn
>> On Tue, Sep 13, 2016 at 7:27 PM Rick Mann via swift-users <swift-users at swift.org> wrote:
>> I'm trying to write this function. The errorHandler: parameter is modeled after the NSFileManager enumerate() function. If I include the @escaping you see there, I get the error "@escaping may only be applied to parameters of function type".
>> 
>> The second parameter, iterator:, seems to have no problems with @escaping.
>> 
>> func
>> iterate(directory inURL: URL?,
>>         includingPropertiesForKeys: [URLResourceKey]? = nil,
>>         options: FileManager.DirectoryEnumerationOptions = [],
>>         errorHandler inErrorHandler: (@escaping (URL, Error) -> Bool)? = nil,
>>         iterator inIterator: (@escaping (URL) throws -> ())) rethrows
>> {
>> }
>> 
>> I'm not sure why I can't apply @escaping here. Can anyone enlighten me? Thank you.
>> 
>> --
>> Rick Mann
>> rmann at latencyzero.com
>> 
>> 
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> 


-- 
Rick Mann
rmann at latencyzero.com