[swift-evolution] Request for Discussion: Setup closures

Adrian Zubarev adrian.zubarev at devandartist.com
Sun Dec 6 05:59:16 CST 2015

I come across this topic and I instantly was overwhelmed by this idea of the Setup Closures. I build a little extension just to test it with UIKit. I thought adding this keyword for Setup Closures was a good idea. If we also could remove this in from the closure it would look good on my opinion.

protocol SettableType {
    init() // designated initializer

extension SettableType {
    init(@noescape setup: (this: Self) -> Void) {
        setup(this: self)

extension UIView: SettableType {}

let view = UIView()

let questionLabel = UILabel() { this in /// <- REMOVE  
    this.textAlignment = .Center
    this.font = UIFont(name:"SomeFontName", size: 72)
    this.text = "Hello World"
    this.numberOfLines = 0

Regards Adrian

Am 6. Dezember 2015 bei 01:16:31, ilya via swift-evolution (swift-evolution at swift.org) schrieb:

> 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

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

Actually I would be happy with something like

let questionLabel = UILabel() .{
    ..textAlignment = .Center
    ..font = UIFont(name:"DnealianManuscript", size: 72)
    ..text = currentQuestion.questionText
    ..numberOfLines = 0

Other thoughts?

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