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Nick keers
Nick keers

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Learning Swift - Part 1

My first post! I've just bought a subscription to to get access to their iOS and Android tutorials. I've been interested in writing apps for a while, but have never really got around to it, so I thought I'd finally try and start learning.

I've worked through part of the Udacity course "Developing Android Apps with Kotlin", but I'm a bit fatigued with the JVM platform at the moment after stepping outside of my element at work and writing a bit of Scala, so I thought I'd try out some Swift instead.

Some background

At work I write code predominantly in Elixir - creating (distributed) systems that can cope with large amounts of traffic - and Go for writing smaller API's / useful applications like load testers and such.

I'm mainly interested in functional programming, so I'm interested to see how I can write some functional code in Swift and to see how that compares to Elixir.

As a first test, I'm going to try and solve a very simple problem in Swift and compare it against an Elixir solution.

The task

Lets try a really simple task first: given a list of numbers 1..100, sum every number that is a multiple of 3 or 5 - but not including numbers that are a multiple of 3 AND 5.

Here's how it looks in Elixir:

|> Enum.filter(fn n -> 
     (rem(n, 3) == 0 or rem(n, 5) == 0) and rem(n, 15) != 0
|> Enum.sum
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That gives us 2103, and the code is not too shabby! The main ugliness here is we have to group the clause for checking the multiple of 3 or 5 separate from the clause for checking if the number is divisible by 15. Lets see how it looks in Swift.

([Int](1...100)).filter { (n) -> Bool in
    (n % 3 == 0) || (n % 5 == 0)
}.filter { (n) -> Bool in
    n % 15 != 0
}.reduce(0, {$0 + $1})
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I struggled to write this a bit in a Swift playground as I'm very new to it, I had to fight the compiler a lot. First I tried to mimic my Elixir code with the range, by just typing

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But it looks like this creates a Swift Range type, which I need to cast to an Array to use filter and reduce with - although I'd love to be corrected here.

I initially had the two filters as just one call, like in the Elixir, but the Swift compiler was telling me that it couldn't type-check it and I need to break it into smaller expressions - that's not very encouraging, I hope that's to do with running it in the playground and not indicative of the Swift compiler itself; although I guess it makes the code more clear.

And last but not least, I'm disappointed there's no sum function, but I can live without one when there's a function shorthand, which is actually fairly similar to Elixir {$0 + $1} vs &(&1 + &2) for example.


Its too early to say much right now, I hope that when I get to using XCode properly and writing some basic apps I won't be hamstrung by the compiler.

I like the syntax for higher order functions though, it's quite readable, and the function shorthand is concise which is great.

Until next time!

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