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Writing A Generic Stable Sort

One more post on writing generic algorithms. Let’s take a non-trivial non-generic algorithm and write a generic version. We’ll use a Java version of merge sort, and also look at some other interesting things we might do to a Java algorithm when converting it to Swift. Why bother with a merge sort? Well, the standard library comes with a very efficient in-place sort, based on the introsort, but…

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Arrays, Linked Lists and Performance

Patient: Doctor doctor, it hurts when I do this. Doctor: Well, don’t do that. On twitter, I wrote: Your reminder that building arrays with reduce, while fun, is accidentally quadratic. I was surprised at how surprising some found this. Quite a few people suggested the reduce version could be changed to not do the array copy (I don’t think it can). Some suggested maybe + could be optimized so it…

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Changes to the Swift standard library in 2.0 betas 2..<5

So, I was waiting for enough library changes accross a few betas to justify posting something, and then all of a sudden lots of stuff changed! So let’s start with: Flat Map Missed from my 2.0b1 changes post (shame on me) was a third kind of flatMap. 1.2 brought us flatMap for collections – given an array, and a function that transforms elements into arrays, it produces a new array with every…

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#swift #swift standard library

A Persistent Tree using indirect enums in Swift

Suppose you want an ordered set. Set is great and all, but it’s unordered. You could always use a Set anyway, and sort the contents when needed. Or you could use an array, keep it sorted, and always insert new elements in the right place. Or, you could use a tree. One way to build a tree in Swift would be with a class that refers to itself. Something like this for a binary search tree: class Tree…

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#collections #functional programming #swift

Protocol extensions and the death of the pipe-forward operator

So a while back I wrote about using some functional programming techniques in Swift to solve the Luhn credit card checksum problem. One of the suggestions in the article was defining and using to |> to avoid the annoying tennis-match bouncing left and right between free functions and methods. Since 2.0 came out, I’ve been thinking I really needed to update some of my articles to the new syntax,…

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A Swift Spelling Corrector

One of my favourite blog posts is Peter Norvig’s How to Write a Spelling Corrector, in which he writes 21 lines of python that sucks in a large corpus of text, and then uses some probability theory to propose spelling corrections. Go read it now, it’s cool.

Anyway, that code has been translated into multiple different programming languages, but not Swift, so let’s give that a go. The resulting…

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Changes to the Swift Standard Library in 1.2 beta 1

Swift v1.2 is out, and, well, it’s pretty fab actually.

The most exciting part for me is the beefed-up if let syntax. Not only does it allow you to unwrap multiple optionals at once, you can define a later let in terms of an earlier one. For instance, here are 3 functions, each one of which takes a non-optional and returns an optional, chained together:

if let url = NSURL(string: urlString),…

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#swift #swift standard library

More fun with implicitly wrapped non-optionals

As we’ve seen previously, Swift will happily auto-wrap your non-optional value inside an optional temporarily if it helps make the types involved compatible. We’ve seen the occasional instance where this can be surprising. But for the most part, this implicit wrapping of non-optionals is your friend.1 Here’s a few more examples.

Equating Optionals

The Swift standard library defines an ==operat…

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#collections #optionals #swift #swift standard library

Avoid using var with this one weird trick

Ever find yourself having to use var when a let would be better, because you’re having to choose between multiple options?

var direction: Direction switch (char) { case "a": direction = .Left case "s": direction = .Right default: direction = .Forward } var cry: String if direction == .Forward { cry = "To glory!" } else { cry = "Tum-tee-tum" }

Often you’ll see people…

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#immutability

zipWith, pipe forward, and treating functions like objects

zipWith and treating functions like any other variable

In the previous article, about implementing the Luhn algorithm using function composition in Swift, I had a footnote to the part about using mapEveryNth to double every other digit:

An alternative could be a version of map that cycled over a sequence of different functions. You could then give it an array of two functions – one that did nothing, and another that did the conversion.

This post…

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#functional programming #swift

A straw man argument for more trying functional programming in Swift

A straw man argument for trying functional programming in Swift

A few weeks back, @SwiftLDN ran a hands-on, and the problem was a calculation of the Luhn checksum for credit card numbers in Swift. Implementing this algorithm features as an early problem to solve in some functional programming tutorials, and can serve as a nice example for contrasting different programming styles.

(If you’re already familiar with more functional-style swift, you might find…

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Running Totals and Force Unwraps

Running Totals

Recently, while implementing my game of immutable snake, I needed to write a function that produced an array of running totals.1 Since creating an array with reduce is all the rage these days, my first take was like this:

let start = 0 let array = [1,2,3] let runningTotal = reduce(array, [start]) { $0 + [$0.last! + $1] } // produces [0,1,3,6]

As you can see, that code snippet contains a force…

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Which function does Swift call? Part 6: Tinkering with priorities

This is part of a series of posts on how Swift resolves ambiguity in overloaded functions. You can find Part 1 here. In the previous article, we looked at why you get a Range from the ... by default. The answer? Because Range has some extra validation that relies on the ... input being comparable, and this makes the Range version more specific.

Defaulting to Neither

So, suppose you didn’t want

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#overloading #swift

Which function does Swift call? Part 5: Range vs Interval

This is part of a series of posts on how Swift resolves ambiguity in overloaded functions. You can find Part 1 here. In the previous article, we looked at how generics are handled.

So finally…

Now that we’ve covered how generics fit in, we can finally answer the original question – how come you get a Range back from 1...5 by default? To recap the sample code:

// r will be of type Range let r =…

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#overloading #swift

Which function does Swift call? Part 4: Generics

This is part 4 of a series on how overloaded functions in Swift are chosen. Part 1 covered overloading by return type, part 2 was about how different functions with simple single arguments were picked on a “best match” basis, and part 3 went into a little more detail about protocols.

We started the series with the question, why do you get a Range type back from 1...5 instead of a ClosedInterval?…

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#overloading #swift

Which function does Swift call? Part 3: Protocol Composition

Previously, we looked at how Swift functions can be overloaded just by return type, and how Swift picks between different possible overloads based on a best-match mechanism.

All this was working towards the reason why 1...5 returns a Range rather than a ClosedInterval. And to understand that, we’ll have to look at how generics fit into the matching criteria.

But before we do, a brief diversion…

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#overloading #swift

Changes to the Swift Standard Library in 1.1 beta 3

The biggest deal in this latest beta is the documentation. There are 2,745 new lines of /// comments in beta 3, and even pre-existing documentation for most items have been revised.

That doesn’t mean there aren’t any functional changes to the library, though. Here’s a rundown of what I could find:

As mentioned in the release notes, the various literal convertible protocols are now implemented as

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#swift #swift standard library

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