[swift-evolution] [Proposal] Factory Initializers
Erica Sadun
erica at ericasadun.com
Mon Jun 5 09:59:26 CDT 2017
Any chance at a 4.1 or a 4.2 round this year?
-- E
> On Jun 5, 2017, at 1:16 AM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org> wrote:
>
> I hope so! We'll have to wait a bit for the core team to outline Swift 5 priorities.
>
>
> On Mon, Jun 5, 2017 at 00:24 Pranshu Goyal <pranshu.goyal at novanet.net <mailto:pranshu.goyal at novanet.net>> wrote:
> Any hopes for it in future?
>
> On 4 June 2017 at 20:40, Xiaodi Wu <xiaodi.wu at gmail.com <mailto:xiaodi.wu at gmail.com>> wrote:
> No.
>
>
>
> On Sun, Jun 4, 2017 at 10:07 Pranshu Goyal via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> Is this proposal in the pipeline for Swift 4?
>
> On 1 April 2017 at 12:03, Adrian Zubarev via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> First, you should fix the indent in the code samples. Second, remove any access modifier from inside a protocol. Third, we don’t support default implementations directly inside protocols yet, so that’s a not valid example.
>
> Now my personal concerns. As far as I can tell XIB files in an iOS Project are meant for UIViewControllers in first place, but it’s a common case that they are also used to create reusable UIViews. The downside of that abusage is view hierarchy clustering. Most developer creating a view of Self in Self, which smells to me like really bad code.
>
> MyCustomView // This view is useless
> + MyCustomView
> + CustomSubview1
> + CustomSubview1 // This is probably a dead IBOutlet
> In fact Xcode does not use the initializer from NSCoding to show a live rendered view inside interface builder, instead it will call a UIViews designated initializer init(frame:). That results that a lot of the developer write similar code like in the following snippet:
>
> // This pattern results in a similar view cluster like mentioned above
>
> class MyCustomView : UIView {
> override init(frame: CGRect) {
> let view = loadSomehowFromNib()
> self.addSubview(view)
> }
> }
> To solve this problem we’d need some functionality of factory initializers. I believe as proposed the factory initializer won’t solve that problem, because everything would be still restricted to a special initializer annotated with factory.
>
> Personally I would want to write something like this instead.
>
> class MyCustomView : UIView {
>
> override init(frame: CGRect) {
>
> // Instantiating from a Nib file will call `init(coder:)` on MyCustomView
> self = loadSomehowFromNib() // assuming () -> MyCustomView
>
> //
> self.frame = frame
> }
> }
> This should resolve the clustering issue by assigning the returned instance from the function to self and create a correct view hierarchy.
>
> + MyCustomView
> + CustomSubview1
>
>
>
> --
> Adrian Zubarev
> Sent with Airmail
>
> Am 17. März 2017 um 17:26:29, Riley Testut via swift-evolution (swift-evolution at swift.org <mailto:swift-evolution at swift.org>) schrieb:
>
>> Hi again everyone!
>>
>> Now that Swift 4 Stage 2 proposals are being considered, I thought it might be time to revisit this proposal and see if it might align with the goals set forth for Swift 4.
>>
>> As a quick tl;dr, this proposal describes a new "factory initializer" that would allow you to return a value from an initializer. This would have several benefits, as mentioned in the proposal itself as well as throughout this mailing list. For convenience, here's a link to the proposal on GitHub: https://github.com/rileytestut/swift-evolution/blob/master/proposals/NNNN-factory-initializers.md <https://github.com/rileytestut/swift-evolution/blob/master/proposals/NNNN-factory-initializers.md>
>>
>> Would love to hear any more comments on this proposal, and if we feel this is appropriate for considering for Swift 4 I'll happily re-open the pull request!
>>
>> Riley Testut
>>
>> On Nov 19, 2016, at 7:45 AM, arkadi daniyelian <arkdan at icloud.com <mailto:arkdan at icloud.com>> wrote:
>>
>>> i would appreciate this feature.
>>>
>>> For unexperienced developers, its often hard to recognize *when* factory is a good fit to do the job, and how exactly approach the implementation. I imagine having this feature built into the language may help to choose and implement factory when its the right thing to do.
>>>
>>>> On Nov 18, 2016, at 12:23 AM, Charles Srstka via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>
>>>> Is there any chance of reviving this? It seems to me that since this would require Swift initializers to be implemented internally in such a way that they can return a value (as Objective-C init methods do), it may affect ABI stability and thus may be germane to the current stage of Swift 4 development.
>>>>
>>>> Charles
>>>>
>>>>> On Dec 17, 2015, at 3:41 PM, Riley Testut via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>>
>>>>> Recently, I proposed the idea of adding the ability to implement the "class cluster" pattern from Cocoa (Touch) in Swift. However, as we discussed it and came up with different approaches, it evolved into a functionality that I believe is far more beneficial to Swift, and subsequently should be the focus of its own proposal. So here is the improved (pre-)proposal:
>>>>>
>>>>> # Factory Initializers
>>>>>
>>>>> The "factory" pattern is common in many languages, including Objective-C. Essentially, instead of initializing a type directly, a method is called that returns an instance of the appropriate type determined by the input parameters. Functionally this works well, but ultimately it forces the client of the API to remember to call the factory method instead, rather than the type's initializer. This might seem like a minor gripe, but given that we want Swift to be as approachable as possible to new developers, I think we can do better in this regard.
>>>>>
>>>>> Rather than have a separate factory method, I propose we build the factory pattern right into Swift, by way of specialized “factory initializers”. The exact syntax was proposed by Philippe Hausler from the previous thread, and I think it is an excellent solution:
>>>>>
>>>>> class AbstractBase {
>>>>> public factory init(type: InformationToSwitchOn) {
>>>>> return ConcreteImplementation(type)
>>>>> }
>>>>> }
>>>>>
>>>>> class ConcreteImplementation : AbstractBase {
>>>>>
>>>>> }
>>>>>
>>>>> Why exactly would this be useful in practice? In my own development, I’ve come across a few places where this would especially be relevant:
>>>>>
>>>>> ## Class Cluster/Abstract Classes
>>>>> This was the reasoning behind the original proposal, and I still think it would be a very valid use case. The public superclass would declare all the public methods, and could delegate off the specific implementations to the private subclasses. Alternatively, this method could be used as an easy way to handle backwards-compatibility: rather than litter the code with branches depending on the OS version, simply return the OS-appropriate subclass from the factory initializer. Very useful.
>>>>>
>>>>> ## Protocol Initializers
>>>>> Proposed by Brent Royal-Gordon, we could use factory initializers with protocol extensions to return the appropriate instance conforming to a protocol for the given needs. Similar to the class cluster/abstract class method, but can work with structs too. This would be closer to the factory method pattern, since you don’t need to know exactly what type is returned, just the protocol it conforms to.
>>>>>
>>>>> ## Initializing Storyboard-backed View Controller
>>>>> This is more specific to Apple Frameworks, but having factory initializers could definitely help here. Currently, view controllers associated with a storyboard must be initialized from the client through a factory method on the storyboard instance (storyboard. instantiateViewControllerWithIdentifier()). This works when the entire flow of the app is storyboard based, but when a single storyboard is used to configure a one-off view controller, having to initialize through the storyboard is essentially use of private implementation details; it shouldn’t matter whether the VC was designed in code or storyboards, ultimately a single initializer should “do the right thing” (just as it does when using XIBs directly). A factory initializer for a View Controller subclass could handle the loading of the storyboard and returning the appropriate view controller.
>>>>>
>>>>> Here are some comments from the previous thread that I believe are still relevant:
>>>>>
>>>>>
>>>>>> On Dec 9, 2015, at 1:06 PM, Philippe Hausler <phausler at apple.com <mailto:phausler at apple.com>> wrote:
>>>>>>
>>>>>> I can definitely attest that in implementing Foundation we could have much more idiomatic swift and much more similar behavior to the way Foundation on Darwin actually works if we had factory initializers.
>>>>>
>>>>>
>>>>>> On Dec 7, 2015, at 5:24 PM, Brent Royal-Gordon <brent at architechies.com <mailto:brent at architechies.com>> wrote:
>>>>>>
>>>>>> A `protocol init` in a protocol extension creates an initializer which is *not* applied to types conforming to the protocol. Instead, it is actually an initializer on the protocol itself. `self` is the protocol metatype, not an instance of anything. The provided implementation should `return` an instance conforming to (and implicitly casted to) the protocol. Just like any other initializer, a `protocol init` can be failable or throwing.
>>>>>>
>>>>>> Unlike other initializers, Swift usually won’t be able to tell at compile time which concrete type will be returned by a protocol init(), reducing opportunities to statically bind methods and perform other optimization tricks. Frankly, though, that’s just the cost of doing business. If you want to select a type dynamically, you’re going to lose the ability to aggressively optimize calls to the resulting instance.
>>>>>
>>>>>
>>>>> I’d love to hear everyone’s thoughts on this!
>>>>>
>>>>> Best,
>>>>> Riley Testut
>>>>> _______________________________________________
>>>>> swift-evolution mailing list
>>>>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
>>>>
>>>> _______________________________________________
>>>> swift-evolution mailing list
>>>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>>>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
>
>
>
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
>
>
>
>
> --
> Pranshu Goyal
> iOS Developer
> tlkn
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
>
>
>
> --
> Pranshu Goyal
> iOS Developer
> tlkn
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20170605/4abffd1d/attachment.html>
More information about the swift-evolution
mailing list