Favorite Swift Tips & Tricks of 2014

Swift allows for a much more functional programming approach when structuring iOS applications, so I’ve been learning a lot about functional programming in order to make better decisions for my Swift code. Here are some of my favorite functional swift resources so far:

Functional Functions - This one easy change to your functions will make your code a lot more independent and testable.

Wrapper Types - I love how readable and safe typealiasing can make code

The Design of Types - More on designing your program with the right types! “Designing the right types for your problem is a great way to help the compiler debug your program”

Practical Use for Curried Functions in Swift - In Haskell, a function can only take one parameter! While Swift is not that extreme, it does allow for “currying” or partially applying a function, which leads to more re-useable pieces of code.

Error Handling in Swift: Might and Magic - I love the simplicity, readability, and safety of this approach to error handling, especially compared to what we usually do in Objective-C.

Railway oriented programming (video here) - This is in F#, but it’s a great way to think about error handling in code - just design for the happy path!

Functional Programming in Swift - This is a bit more advanced book on the functional swift topic, but I’ve found myself finding something new here every time I re-read it. Great for those who’d like a lot more depth and exposure into functional world and how to apply the concepts to iOS code.

Watch Natasha’s video: Building TableViews in Swift & iOS8

Functional Quicksort — the following variant of Quicksort will definitely not win any speed prize. Most real implementations of Quicksort will use constant memory. This snippet, however, is one of the shortest and clearest ways to write Quicksort:

func qsort(input: [Int]) -> [Int] {
    if let (pivot, rest) = input.decompose {
        let lesser = rest.filter { $0 < pivot }
        let greater = rest.filter { $0 >= pivot }
        return qsort(lesser) + [pivot] + qsort(greater)
    } else {
        return []
    }
}

It builds on the decompose snippet: if the array is not empty, it uses the first element as the pivot, and seperates the array into two new arrays: the first containing only smaller elements, and the second containing only larger (or equal) elements. Then it sorts the smaller elements, appends the pivot element, and finally appends the sorted larger elements.

Originally appeared on http://www.objc.io/snippets/3.html

Watch Chris’ video: Functional Programming in Swift

A nifty (if rather useless) Swift trick that I like is the fact that you can set a delegate to an instance of an anonymous class by creating a closure that defines a conforming class, having that closure return a new instance of that class, and running the closure. That sounds complicated, and so I have a bit of sample code here.

You can watch Austin’s videos: Swift: Enums, Pattern Matching & Generics & Lessons Learned Building “2048” in Swift, or check out his blog.

Here’s my essential bash alias for dealing with all problems xcode (and particularly sourcekit issues):

alias sourcekitsad='rm -rf ~/Library/Developer/Xcode/DerivedData'

You can watch Clay’s 12 Apps of Swiftmas video, or check him out on GitHub.

Favorite bit of trivia would probably be that String does not conform to Printable, so there’s technically not a guarantee that string interpolation works with a String. I think it only works because String is bridged to NSString, which does have a -description method.

You can watch Michael’s 12 Apps of Swiftmas presentation, or check out his blog.

Swift seems elegant enough as a language that I don’t particularly find myself needing to hack with special tricks. I do like using enums together with raw types, like this:

public enum ReminderTimeType: String {
    case Evening = "this evening"
    case Tomorrow = "tomorrow"
    case Weekend = "this weekend"
    case NextWeek = "next week"
    case CoupleWeeks = "in a couple weeks"
    case CoupleMonths = "in a couple months"
    case Someday = "someday"
    
    public static let array = [
        Evening, Tomorrow, Weekend, NextWeek, CoupleWeeks, CoupleMonths, Someday
    ]
    
    public static let rawArray = array.map { $0.rawValue }
}

You can watch David’s video: Converting Objective-C to Swift, or check him out on GitHub.

My favorite piece of Swift trivia, trick, resource, or anything? My two favorite tricks of the moment: On the REPL, the handy function

func typeof<T>(@autoclosure () -> T) -> Any.Type { return T.self }

can be used to get the static type of an expression without evaluating the expression. And the undocumented private function _stdlib_getDemangledTypeName can be used to get the type name of any instance value.

You can watch Alexis’ 12 Apps of Swiftmas presentation, or follow him on Twitter @alexisgallagher.

You can get all the private Swift standard library functions by digging through libswiftCore.dylib using the nm tool like this:

```bash
cd `xcode-select -p`/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/macosx
nm -a libswiftCore.dylib | grep "T _swift_stdlib_"
```

Which reveals some very useful functions like _stdlib_getTypeName(), _stdlib_demangleName() and _stdlib_conformsToProtocol() among a few others.

You can watch JP’s videos: Swift for JavaScript Developers & Swift for Rubyists.

This is kind of a hack, but it turns out that Swift allows you to treat a homogeneous array of structs as a pointer to the member type of the struct, when all the members of the struct are of the same type (e.g., Float). I use this to succinctly create Metal buffers of vertex data without a lot of unsightly casting.

My favorite Swift resource is this: Swifter (great reference guide when I’m coding)

Favorite piece of Trivia: You can enable dynamic dispatch on any swift func to enable objective-C style dynamic dispatching.