[swift-users] Swift 3 (Xcode 8 GM) issue with @escaping

[Jacob Bandes-Storch]

On Wed, Sep 7, 2016 at 5:54 PM, Michael Ilseman via swift-users <
swift-users at swift.org> wrote:

> I implemented a better (i.e. correct) diagnostic message for this at
> https://github.com/apple/swift/pull/4670. I want to also do a better
> diagnostic specifically for aggregate parameters to functions (e.g.
> optional closures), but that requires more work in the type checker.
>
> Basically, @escaping is valid only on closures in function parameter
> position. The noescape-by-default rule only applies to these closures at
> function parameter position, otherwise they are escaping. Aggregates, such
> as enums with associated values (e.g. Optional), tuples, structs, etc., if
> they have closures, follow the default rules for closures that are not at
> function parameter position, i.e. they are escaping.
>

Shouldn't it be possible to allow distinguishing @escaping/@noescape for
aggregates like these, at least for the simple case of Optional?  (I
handled optionals in https://github.com/apple/swift/pull/4438 for imported
function types; see comment
<https://github.com/apple/swift/pull/4438#issuecomment-243645367>.)


>
> It would be a post-Swift-3 addition to the language to be able to support
> more robust liveness tracking here. There may be interesting directions to
> take this, with optional closures being the most common beneficiary.
>
> On Sep 7, 2016, at 3:33 PM, Shawn Erickson via swift-users <
> swift-users at swift.org> wrote:
>
> I see https://bugs.swift.org/browse/SR-2324 and
> https://bugs.swift.org/browse/SR-2444 which looks related to this issue
> and may explain the error I saw on "the other side" of this.
>
>
>
> On Wed, Sep 7, 2016 at 3:28 PM Shawn Erickson <shawnce at gmail.com> wrote:
>
>> Yeah I actually have a few of those myself that I can no longer do.
>>
>> On Wed, Sep 7, 2016 at 3:26 PM Jon Shier <jon at jonshier.com> wrote:
>>
>>> Perhaps relatedly, it no longer seems possible to mark typealiased
>>> closures as @escaping. That was quite handy when you know that closures
>>> will always be used asynchronously.
>>>
>>>
>>> Jon
>>>
>>>
>>> On Sep 7, 2016, at 6:15 PM, Shawn Erickson via swift-users <
>>> swift-users at swift.org> wrote:
>>>
>>> I should note that this issue also appeared in an earlier variant of
>>> Swift after the addition of @escaping but I was on vacation so didn't get a
>>> chance to report it then. It isn't new with the Xcode 8 GM.
>>>
>>> On Wed, Sep 7, 2016 at 3:08 PM Shawn Erickson <shawnce at gmail.com> wrote:
>>>
>>>> I like and fully supported the change to @escaping away from @noescape
>>>> however in a body of code that I am porting to the latest Swift 3 variant
>>>> (as found in Xcode 8 GM) I am hitting an issue for methods that take an
>>>> optional completion closure. If optional is involved I can't find a way to
>>>> apply @escape to the escaping closure. See the following for an basic
>>>> example...
>>>>
>>>> Is their a way to do what I need and/or is this an edge case in the
>>>> implementation of @escaping?
>>>>
>>>> typealias MyCallback = (String)->()
>>>>
>>>> // Happy
>>>> func foo1(bar: String, completion: ((String)->())) {
>>>>     completion(bar)
>>>> }
>>>>
>>>> // Happy
>>>> func foo2(bar: String, completion: MyCallback) {
>>>>     completion(bar)
>>>> }
>>>>
>>>> // Happy
>>>> func foo3(bar: String, completion: ((String)->())? = nil) {
>>>>     completion?(bar)
>>>> }
>>>>
>>>> // Happy
>>>> func foo4(bar: String, completion: MyCallback? = nil) {
>>>>     completion?(bar)
>>>> }
>>>>
>>>> // Happy
>>>> func foo5(bar: String, completion: Optional<MyCallback> = nil) {
>>>>     completion?(bar)
>>>> }
>>>>
>>>> // Happy
>>>> func foo6(bar: String, completion: @escaping (String)->()) {
>>>>     completion(bar)
>>>> }
>>>>
>>>> // Happy
>>>> func foo7(bar: String, completion: @escaping MyCallback) {
>>>>     completion(bar)
>>>> }
>>>>
>>>> // Unhappy...
>>>> // "@escaping attribute only applies to function types"
>>>> func foo8(bar: String, completion: @escaping ((String)->())? = nil) {
>>>>     completion?(bar)
>>>> }
>>>>
>>>> // Unhappy...
>>>> // "@escaping attribute only applies to function types"
>>>> func foo9(bar: String, completion: @escaping MyCallback? = nil) {
>>>>     completion?(bar)
>>>> }
>>>>
>>>> // Unhappy...
>>>> // "@escaping attribute only applies to function types"
>>>> func foo10(bar: String, completion: (@escaping ((String)->()))? = nil) {
>>>>     completion?(bar)
>>>> }
>>>>
>>>> // Unhappy...
>>>> // "@escaping attribute only applies to function types"
>>>> func foo11(bar: String, completion: (@escaping MyCallback)? = nil) {
>>>>     completion?(bar)
>>>> }
>>>>
>>>> // Unhappy...
>>>> // "@escaping attribute only applies to function types"
>>>> func foo12(bar: String, completion: Optional<@escaping MyCallback> =
>>>> nil) {
>>>>     completion?(bar)
>>>> }
>>>>
>>> _______________________________________________
>>> swift-users mailing list
>>> swift-users at swift.org
>>> https://lists.swift.org/mailman/listinfo/swift-users
>>>
>>>
>>> _______________________________________________
> swift-users mailing list
> swift-users at swift.org
> https://lists.swift.org/mailman/listinfo/swift-users
>
>
>
> _______________________________________________
> swift-users mailing list
> swift-users at swift.org
> https://lists.swift.org/mailman/listinfo/swift-users
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-users/attachments/20160907/d7524e2f/attachment.html>