[swift-evolution] Request for Discussion: Setup closures

Matthew Johnson matthew at anandabits.com
Sun Dec 6 20:04:05 CST 2015 

I do agree that current approaches are a bit ugly, that they are common in Cocoa code, and that the proposal cleans this up.  I would even enjoy the cleaner syntax in my own code if the feature was adopted.

However, I share Jacob's thought that focusing on improving initialization flexibility is where we should focus.  I think it is a better use of our time, effort and language feature "budget".  This might be a more complex problem to solve, but the payoff is much larger in the end.

Ideally instances should be fully configured for their intended use when initialization completes.  I view the *need* for post-initialization setup as a deficiency in the language, the interface of the type, or both (even if a type must expose members that are mutated by users during the lifetime of an instance it should still be possible to fully configure an instance for its initial use during initialization).  

If we can remove the aforementioned deficiency we will not need "setup closures". Doing this will require a language feature as well as a way to take advantage of the new feature when using Cocoa (probably through the Objective-C API import mechanism).

We obviously need to begin with the language feature so that is where I'm focusing right now.  I plan to write a first draft of a proposal soon.

All of this aside, I am still interest in hearing about additional use cases for the "method cascade" idea.  If it is more broadly applicable I might find it more worthwhile.

Sent from my iPhone

> On Dec 6, 2015, at 3:13 PM, Jacob Bandes-Storch via swift-evolution <swift-evolution at swift.org> wrote:
> 
> It seems like setting properties just after init is the main use case here.
> 
> I'm not against this idea, but I want to point out that this doesn't *need* to be solved by a change to the language. You can easily define a convenience init for UILabel that takes textAlignment, font, text, and numberOfLines as parameters. They could have default values so you can specify just the ones you need.
> 
> I like the idea of being able to do configure objects/values conveniently, but I'm not sure how to justify a language change for it. Perhaps we just need better autogeneration of initializers during Obj-C header import.
> 
> Jacob Bandes-Storch
> 
>> On Sun, Dec 6, 2015 at 1:06 PM, Erica Sadun via swift-evolution <swift-evolution at swift.org> wrote:
>> Do you want me to tweak that? Or remove it entirely? Also, I think I forgot to name-drop you slightly earlier as well
>> 
>>> On Dec 6, 2015, at 2:04 PM, David Waite <david at alkaline-solutions.com> wrote:
>>> 
>>> I’m leaning away from “self in” style syntax - I think there are too many cases where you still want to be able to bind and access the self of the object your closure was declared within.
>>> 
>>> I’m not sure you have to establish a new “self” however - have the type of object given to with is known, so the methods/functions available to it can be exposed as lexical scope. 
>>> 
>>> To keep code clarity, use of methods/functions which shadow something in higher lexical scope should likely result in compiler errors.
>>> 
>>> -DW
>>> 
>>>> On Dec 6, 2015, at 1:48 PM, ilya via swift-evolution <swift-evolution at swift.org> wrote:
>>>> 
>>>> I applaud honest description of drawbacks in the proposal :) 
>>>> 
>>>> There examples given, I think, demonstrate that using self without any special access leads to unresolvable ambiguities. 
>>>> 
>>>> If one wants to work "inside" the configured object, this seems like a good job for a private initializer. All of the ambiguities will be resolved, because extracting the init away removes its ability to capture names from the local context. 
>>>> 
>>>> Alternatively, I think it makes sense to continue working on configuration syntax, with "default" access to local context and "explicit" access to the object. Let's just replace $0 with something else. 
>>>> 
>>>> Hopefully I don't sounds too pessimistic. Erica's proposal looks going in the right direction to me. 
>>>>> On Sun, Dec 6, 2015 at 23:30 Erica Sadun via swift-evolution <swift-evolution at swift.org> wrote:
>>>>> It's probably better at this point for me to collect my thoughts and summarize where I am at.
>>>>> 
>>>>> https://gist.github.com/erica/eb32feb22ba99629285a
>>>>> 
>>>>> Please feel free to comment on-list about this proposal (github does not forward comment alerts) and
>>>>> then I will start a new list thread as a Proposal rather than as a Request for Discussion.
>>>>> 
>>>>> Best,
>>>>> 
>>>>> -- E
>>>>> 
>>>>> 
>>>>>> On Dec 6, 2015, at 12:45 PM, ilya <ilya.nikokoshev at gmail.com> wrote:
>>>>>> 
>>>>>> Sorry, did I misunderstand the question? 
>>>>>> 
>>>>>> Did you asked whether my definition will work for immutable value types? 
>>>>>> If that's the question, the answer is still yes, the link has an example :) 
>>>>>> 
>>>>>>> On Sun, Dec 6, 2015 at 10:43 PM, Erica Sadun <erica at ericasadun.com> wrote:
>>>>>>> I was specifically referring to value types. I apologize for not being clearer.
>>>>>>> 
>>>>>>> -- E
>>>>>>> 
>>>>>>> 
>>>>>>>> On Dec 6, 2015, at 12:42 PM, ilya <ilya.nikokoshev at gmail.com> wrote:
>>>>>>>> 
>>>>>>>> Yes, it works for immutable objects with the correct definition, see the playground contents at https://github.com/ilyannn/iOS-Swift-Materials/blob/master/Playgrounds/Configure.playground/Contents.swift
>>>>>>>> 
>>>>>>>> On Sun, Dec 6, 2015 at 8:10 PM, Erica Sadun <erica at ericasadun.com> wrote:
>>>>>>>>> I have developed something similar as well (http://ericasadun.com/2015/11/15/speeding-up-swift-playgrounds-with-closure-initialization-swiftlang/).
>>>>>>>>> 
>>>>>>>>> Is yours capable of handling enums and structs that would otherwise be let after declaration because mine is not.
>>>>>>>>> 
>>>>>>>>> -- E
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>>> On Dec 5, 2015, at 5:16 PM, ilya via swift-evolution <swift-evolution at swift.org> wrote:
>>>>>>>>>> 
>>>>>>>>>> > PROBLEM: With many Apple-supplied classes, typical initializers fail to fully set up an instance for use.  Here's one example: ...
>>>>>>>>>> 
>>>>>>>>>> FWIW, I created a configuration operator more then a year ago, and use it in all of my Swift projects:
>>>>>>>>>> 
>>>>>>>>>> let task = NSTask() +=+ {
>>>>>>>>>>     $0.launchPath = "/usr/bin/mdfind"
>>>>>>>>>>     $0.arguments = ["kMDItemDisplayName == *.playground"]
>>>>>>>>>>     $0.standardOutput = pipe
>>>>>>>>>> }
>>>>>>>>>> 
>>>>>>>>>> Note you can also use the configured object in the rhs:
>>>>>>>>>> 
>>>>>>>>>> let questionLabel = UILabel() +=+ {
>>>>>>>>>>     $0.textAlignment = .Center
>>>>>>>>>>     $0.font =  UIFont(name:"DnealianManuscript", size: 72)
>>>>>>>>>>     $0.text = currentQuestion.questionText
>>>>>>>>>>     $0.numberOfLines = 0
>>>>>>>>>>     view.addSubview($0)
>>>>>>>>>> }
>>>>>>>>>> 
>>>>>>>>>> This $0. certainly looks ugly and it would be great to be able to simplify this. I don't llike the following much though (dot-syntax can be ambiguos here, and using simply a method name is even worse):
>>>>>>>>>> 
>>>>>>>>>> let questionLabel = UILabel() +=+ {
>>>>>>>>>>     .textAlignment = .Center
>>>>>>>>>>     .font =  UIFont(name:"DnealianManuscript", size: 72)
>>>>>>>>>>     .text = currentQuestion.questionText
>>>>>>>>>>     .numberOfLines = 0
>>>>>>>>>>     view.addSubview($0)
>>>>>>>>>> }
>>>>>>>>>> 
>>>>>>>>>> Actually I would be happy with something like
>>>>>>>>>> 
>>>>>>>>>> let questionLabel = UILabel() .{
>>>>>>>>>>     ..textAlignment = .Center
>>>>>>>>>>     ..font = UIFont(name:"DnealianManuscript", size: 72)
>>>>>>>>>>     ..text = currentQuestion.questionText
>>>>>>>>>>     ..numberOfLines = 0
>>>>>>>>>>     view.addSubview($0)
>>>>>>>>>> }
>>>>>>>>>> 
>>>>>>>>>> Other thoughts?
>>>>>>>>>> 
>>>>>>>>>>   
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>>>>>>>>>> swift-evolution at swift.org
>>>>>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>> 
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