[swift-evolution] Closure delegation

[Marc Knaup]

How would capture semantics work?

I think this could easily lead to reference cycles as the parameter is
captured strongly without any hint at the call-site.
The developer should be warned and have a way to state the capture
semantics explicitly through the capture list.

If the delegate parameter "Bar" becomes "self" in the closure then using
"self" everywhere should be required just as in normal closures.
"@noescape" would avoid this but the closure reference must be stored then.
If the delegate parameter "Bar" really becomes "self" there's also the
problem that the original "self" variable suddenly becomes hidden.


On Fri, Dec 11, 2015 at 1:15 PM, James Campbell via swift-evolution <
swift-evolution at swift.org> wrote:

>
>
> On Fri, Dec 11, 2015 at 12:14 PM, James Campbell <james at supmenow.com>
> wrote:
>
>> So I don't like this way of declaring it as it is not very clear what it
>> is doing  but I actually prefer the javascript way of binding, so in your
>> example the code would be this:
>>
>> func prepareSomething(setup:() -> ()) {
>>     let bar = BarImplementation()
>>     // code before
>>     setup().bind(bar)
>>     // code after
>> }
>>
>> The bind method lets Swift know it should bind this to `bar`, so now this
>> is the same as writing `bar`. So in your example:
>>
>> without delegation
>> prepareSomething { delegate in
>>     delegate.someConfig = "Hello World"
>> }
>>
>> with binding
>> prepareSomething {
>>     someConfig = "Hello World"
>> }
>>
>> These would work the same :)
>>
>> On Fri, Dec 11, 2015 at 11:49 AM, Pierre Monod-Broca <
>> pierremonodbroca at gmail.com> wrote:
>>
>>> without delegation
>>> prepareSomething { delegate in
>>>     delegate.someConfig = "Hello World"
>>> }
>>>
>>> with delegation
>>> prepareSomething {
>>>     someConfig = "Hello World"
>>> }
>>>
>>> The exemple is not very compelling, but in a manifest file it would
>>> reduce boiler plate.
>>>
>>> Pierre
>>>
>>> Le 11 déc. 2015 à 12:29, James Campbell <james at supmenow.com> a écrit :
>>>
>>> Whats the advantage over this ?
>>>
>>> protocol Bar {
>>>>     var someConfig: String { get set }
>>>> }
>>>>
>>>> func prepareSomething(setup: (delegate: Bar) -> ()) {
>>>>
>>>
>>> On Fri, Dec 11, 2015 at 11:27 AM, Pierre Monod-Broca <
>>> pierremonodbroca at gmail.com> wrote:
>>>
>>>>
>>>> Le 11 déc. 2015 à 11:54, James Campbell <james at supmenow.com> a écrit :
>>>>
>>>> Could you explain a little more its a bit confusing ?
>>>>
>>>> On Fri, Dec 11, 2015 at 10:32 AM, Pierre Monod-Broca via
>>>> swift-evolution <swift-evolution at swift.org> wrote:
>>>>
>>>>> A groovy closure can have a delegate which replaces `this` as the
>>>>> default receiver. The issue in groovy is that it is not compatible with
>>>>> static compilation, and there is no way to know from the code what is the
>>>>> type of the delegate.
>>>>>
>>>>> It works great for DSL. It would work great the Swift Package Manager
>>>>> manifest, among other things.
>>>>>
>>>>> It could look like this in swift
>>>>>
>>>>> protocol Bar {
>>>>>     var someConfig: String { get set }
>>>>> }
>>>>>
>>>>> func prepareSomething(setup: @delegate Bar -> () -> ()) {
>>>>>
>>>> Here we define a function `prepareSomething(_:)` which receives one
>>>> parameter: a closure that takes a delegate conforming to `Bar`, and
>>>> otherwise take no parameter and returns nothing
>>>>
>>>>     let bar = BarImplementation()
>>>>>     // code before
>>>>>     setup(bar)()
>>>>>
>>>> Here we pass a delegate to the closure, then call the closure
>>>>
>>>>     // code after
>>>>> }
>>>>>
>>>>> prepareSomething { () -> () in
>>>>>
>>>> Here we call the function `prepareSomething(_:)` with a closure which
>>>> we define a the same time
>>>>
>>>>     someConfig = "Hello world"
>>>>>
>>>> Here `someConfig` is a property of the closure’s delegate
>>>>
>>>> }
>>>>>
>>>>> Where `someConfig` would refer to bar.
>>>>>
>>>>>
>>>> I’m not sure about the syntax, we could also declare the delegate that
>>>> way, maybe :
>>>> func prepareSomething(doSomething: @delegate(Bar) () -> ()) {
>>>>     /**/
>>>> }
>>>>
>>>> Pierre
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> swift-evolution mailing list
>>>>> swift-evolution at swift.org
>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>>  Wizard
>>>> james at supmenow.com
>>>> +44 7523 279 698
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>> --
>>>  Wizard
>>> james at supmenow.com
>>> +44 7523 279 698
>>>
>>>
>>>
>>
>>
>> --
>>  Wizard
>> james at supmenow.com
>> +44 7523 279 698
>>
>
>
>
> --
>  Wizard
> james at supmenow.com
> +44 7523 279 698
>
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