Functional Swift: Using Array filter and forEach functions

Recently, I started learning a couple of functional languages through online MOOCs:

Swift isn’t classified as a functional language. However, that doesn’t mean we can’t use lessons learned from functional programming to improve our code. In this article, I illustrate a few ways my programming has changed after a couple of weeks of functional programming.

[].filter

There are many places in my code that looked something like this snippet:

self.retestQuestions = []

for q in questionList {
    if !q.isAnsweredCorrectly {
        self.retestQuestions.append(q)
    }
}

This translates to one line of Swift code:

let retestQuestions = questionList.filter({!$0.isAnsweredCorrectly})

In the past, I’ve used filter() to replace NSPredicate statements, which I used extensively in Objective C. In my first conversion to Swift, I directly translated my Objective C to Swift then cast my Swift array back to an NSArray to get the filter to work. Roughly my code looked like this:

let predicate = NSPredicate(format: "numWordsInGroup >= \(minWordCount) and  numPicturesInGroup >= \(minPictureCount)")

let answer = (a1 as NSArray).filtered(using: predicate)

Embracing the Array filter() function makes a lot more sense:

let answer = a1.filter({$0.numWordsInGroup >= minWordCount && $0.numPicturesInGroup >= minPictureCount})

After only a couple of weeks of functional programming, I’ve noticed many places in my code where this example, and other

[].forEach

The forEach() function isn’t a functional concept. However, without going into detail, my functional programming has led me to prefer using the Array forEach function more often. Here are several snippets from my code:

Add subviews to parent

[pronounView, answerWellView, answerConjugationView].forEach {self.mainContainerView.addSubview($0)}

Update: Someone pointed out on Reddit that this can be simplified:

// Simply pass func to apply to each element
[pronounView, answerWellView, answerConjugationView].forEach (mainContainerView.addSubview)

Active constraints

[c1, c2].forEach {NSLayoutConstraint.activate($0)}

Applying the same concept of passing the function as an argument to forEach(), activating constraints is even simpler.

[c1, c2].forEach(NSLayoutConstraint.activate) 

translatesAutoresizingMaskIntoConstraints and addSubviews

[answer1Btn, answer2Btn, answer3Btn, answer4Btn].forEach {
    $0.translatesAutoresizingMaskIntoConstraints = false
    self.cardFrontSubView.addSubview($0)
}

Disable and hide buttons

[answer1Btn,answer1Btn,answer3Btn,answer4Btn].forEach {
    $0.isEnabled = false
    $0.isHidden = false
}

Conclusion

I’ve just finished the second week, of a six week, Haskell MOOC. Hopefully, soon I’ll be using more functional concepts and my code will be “cleaner”, and more importantly contain fewer bugs.

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Disabling Activity Tracing in Xcode 8

In Xcode 8, every time you run your app, there is additional logging information in the debugging window that looks similar to this:

2016-09-29 12:37:04.826400 LosVerbos[24208:17542891] subsystem: com.apple.UIKit, category: HIDEventFiltered, enable_level: 0, persist_level: 0, default_ttl: 0, info_ttl: 0, debug_ttl: 0, generate_symptoms: 0, enable_oversize: 1, privacy_setting: 2, enable_private_data: 0
2016-09-29 12:37:04.833232 LosVerbos[24208:17542891] subsystem: com.apple.UIKit, category: HIDEventIncoming, enable_level: 0, persist_level: 0, default_ttl: 0, info_ttl: 0, debug_ttl: 0, generate_symptoms: 0, enable_oversize: 1, privacy_setting: 2, enable_private_data: 0
2016-09-29 12:37:04.844944 LosVerbos[24208:17542886] subsystem: com.apple.BaseBoard, category: MachPort, enable_level: 1, persist_level: 0, default_ttl: 0, info_ttl: 0, debug_ttl: 0, generate_symptoms: 0, enable_oversize: 0, privacy_setting: 0, enable_private_data: 0

xcode

While this may be useful at some point, I find that it makes it harder to see my own debugging messages. These messages can be disabled by setting an environment variable in your schema: OS_ACTIVITY_MODE disable

 

schema
More on Apple’s new logging: WWDC 2016 – Session 721 – iOS, macOS – Unified Logging and Activity Tracing

My iOS 10 and Swift 3 Refactor List

I used an early beta of Xcode 8 to begin my conversion to Swift 3, which led to some issues so I had to do a lot of manual changes. Actually the conversion tool still works well a line at a time. Next Error followed by Return (CMD-‘, Return) is quite handy.

I thought it would be great to track them and keep a list in one place.

layerClass() method is now a variable:

override public class func layerClass() -> AnyClass {
    return CAEmitterLayer.self
}

override public class var layerClass: AnyClass {
    return CAEmitterLayer.self
}

Method signature in AppDelegate changed to:

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        return true
    }

Still unresolved: ??

CGAffineTransform.scale(transform, scale, scale)
CGAffineTransform.scaledBy(transform, scale, scale) ???
transform = CGAffineTransform(scaleX: scale, y:scale)

CGContextSetRGBStrokeColor(context, 1.0, 0.0, 0.0, 1.0)
context.setStrokeColor(red: 1, green: 0, blue: 1, alpha: 1)
[color getRed:&red0 green:&green0 blue:&blue0 alpha:&alpha0];
       var red0:CGFloat = 0
        var green0:CGFloat = 0
        var blue0:CGFloat = 0
        var alpha0:CGFloat = 0
color.getRed(&red0, green: &green0, blue: &blue0, alpha: &alpha0)
NSMakeRange(col, 1) // Unresolved
substringWithRange()
let x = rowString.substring(with: <#T##Range#>)
UIFont *aFont = [UIFont fontWithName:"American Typewriter" size:fontSize]
let aFont = UIFont(name:"American Typewriter", size:fontSize)
NSDictionary *attributes = @{NSFontAttributeName:  aFont}
let attributes = [NSFontAttributeName:  aFont]
UIRectCornerAllCorners
UIRectCorner.allCorners
xmlText.componentsSeparatedByString("\n")
xmlText.components(separatedBy: "\n")
anArray.joinWithSeparator(",")
anArray.joined(separator: ",")
String(contentsOfURL: xmlUrl)
String(contentsOf: xmlUrl)
url.componentsSeparatedByString("/")
url.components(separatedBy: "/")
"  foobar  ".stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceCharacterSet())
"  foobar  ".trimmingCharacters(in: NSCharacterSet.whitespaces)
NSTextAlignment.Center
NSTextAlignment.center
forState: .Normal
forState: .normal
.TouchUpInside 
.touchUpInside
url.rangeOfString("github.com")
url.contains("github.com")
// https://www.hackingwithswift.com/swift3
stringByReplacingOccurrencesOfString(" ", withString:"_")
"Hello, world".replacingOccurrences(of: "Hello", with: "Goodbye")
// https://swift.org/migration-guide/
DispatchQueue.GlobalAttributes.qosDefault
        DispatchQueue.global(qos: DispatchQoS.QoSClass.default).async {

}

UIApplication.sharedApplication().
UIApplication.shared.

UIDevice.currentDevice().
UIDevice.current.
UIBezierPath(ovalInRect
UIBezierPath(ovalIn

touchesBegan() signature changed?

    override func touchesBegan(_ touches: Set, with event: UIEvent?) {
            if let touch = touches.first {
                let point = touch.location(in: self.superview)
            }

    }

moveToPoint()
move(to:
addLineToPoint()        
addLine(to: 
closePath()
close()
CGGradientCreateWithColors
CGColorSpaceCreateDeviceRGB
drawInRect
.draw(in: 
CGRectGetMaxX
CGRectGetMaxY

self.maxX
self.maxY
CGRectGetMidX()
CGRectGetMidY()

self.midX
self.midY
CGContextStrokePath(context)
context.strokePath()
CGContextSetLineWidth(context, 20)
context.setLineWidth(20)
CGRectInset()
self.bounds.insetBy(dx: 3, dy: 3)
self.view.bringSubviewToFront(cardFront)
self.view.bringSubview(toFront: cardFront)

self.tableView.registerClass(UITableViewCell.self, forCellReuseIdentifier:CellIdentifier)

self.tableView.register(UITableViewCell.self, forCellReuseIdentifier:CellIdentifier)

self.showViewController(viewController, sender: self)
self.show(viewController, sender: self)
lowercaseString
lowercased()
//http://stackoverflow.com/questions/38964264/openurl-in-ios10

UIApplication.shared.openURL(URL(string: appStoreUrl)!)
UIApplication.shared.open(URL(string:appStoreUrl)!, options: [:])

type(of:)

CGColorRef

UIGraphicsPushContext(context);
UIGraphicsPopContext();

context.saveGState()
context.restoreGState()
CalendarIdentifierGregorian
Calendar.Identifier.gregorian
Calendar.currentCalendar()
Calendar.current
CalendarOptions
Calendar.Options
.dateFromComponents()
.date(from:)
.dateByAddingComponents()
Calendar.current.date(byAdding: dateComponents, to: )

Autolayout issue Xcode 8 beta 6: _SwiftValue nsli_superitem

I’m converting my Objective C and Swift 2.x code to Swift 3 and I started getting this strange error:

[_SwiftValue nsli_superitem]: unrecognized selector sent to instance 0x610000056740

This occurred in my NSLayoutConstraint.constraints() methods:

[constraintString1, constraintString2].forEach {

    let constraint = NSLayoutConstraint.constraints(withVisualFormat: $0, options: [], metrics: metrics, views: viewDictionary)

   NSLayoutConstraint.activate(constraint)

}

Currently, I used inferred types on my viewDictionary and metrics variables:

let viewDictionary = [
"answerView1": self.answerView1,
"answerView2": self.answerView2,
"answerView3": self.answerView3,
"answerView4": self.answerView4,
]

let metrics = [:]

The workaround seems to be to provide explicit types on these two variables:

let viewDictionary:[String:UIView] = [
"answerView1": self.answerView1,
"answerView2": self.answerView2,
"answerView3": self.answerView3,
"answerView4": self.answerView4,
]

let metrics:[String:AnyObject] = [:]

There’s probably a deeper issue here but at this point, I’m simply glad to have my app running again. I’ll post more if I figure out any additional details.

5000 Swift URLs

Another 3 months and another 1000 URLs added to the collection.

http://www.h4labs.com/dev/ios/swift.html

There haven’t been any updates to the “search engine” in the past 3 months, and I don’t have much to add at this point that hasn’t already been said in the previous announcements:

https://h4labs.wordpress.com/2016/04/19/4000-swift-urls/

https://h4labs.wordpress.com/2016/01/18/3000-swift-urls/

https://h4labs.wordpress.com/2015/09/10/1500-swift-urls/

Please let me know if anyone has any feature requests.  Also, don’t forget that all the URLs are in a tsv on Github:

https://github.com/melling/SwiftResources

 

 

Ghost in the Microwave

microwave2

This morning our 8 year old (2008) GE microwave started turning on by itself in “Canned Vegetable” mode, a mode I don’t think we’ve ever used. I unplugged it several times for several minutes at a time, hoping the “reboot” might clear it up but it didnt’work.  At this point, I simply don’t trust it.

Anyway, I’m glad I was home. I don’t know if these things can start fires but having the microwave running for hours while we are away can’t be good.  Here’s the microwave information, in case you are experiencing a similar problem:

Model No: JVM1750SM1SS

Made in Malaysia

From what I’ve been reading on the Internet, it seems like the main circuit board is the culprit.

Someone else with the same model had the exact same complaint:

http://www.saferproducts.gov/ViewIncident/1466299

However, it does seem to be a common problem in other GE models:

4000 Swift URLs

The Swift Resources page reached 4000 URLs yesterday.

http://www.h4labs.com/dev/ios/swift.html

It has been 3 months since 3000 URLs, so Swift content is being generated quite quickly. iOS 10 will be announced in less than 2 months. At the current rate, we should expect 1000 iOS 10 Swift blogs and Github projects before it’s released in September.

In addition, over the past few months, I’ve added paywall links, although I haven’t gone back to add all the links. The content created by https://www.raywenderlich.com and http://nsscreencast.com/episodes is exceptional and well worth the money.

Finally, the iOS Swift books now has a search feature and I’m in the process of adding discount codes.

http://www.h4labs.com/dev/ios/books

If you know of a book not on the list, please let me know.

We’re approaching the start of Swift’s third year, and it looks like everything is in place to accelerate its already rapid adoption.