Swift

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Austin Gatlin
October 7, 2023 (last updated September 22, 2024)

Swift pairs well with Apple's XCode IDE when developing for the Apple ecosystem. Particularly useful features of XCode are app previews, device simulations, and running development code on actual Apple devices locally.

First learning Swift reminded me of Kotlin, though I'm not sure why. Perhaps because it a modern OO-friendly language with first-class functional primitives vis-a-vis closures.

Swift, Apple, XCode, SwiftUI, etc

See my note on SwiftUI, which is also the current home of Apple related Swift notes, including XCode notes, etc.

Arrays

I cannot find exact documentation on this, but I was struck by this syntax,

let data: Data = ...
let bytes: [UInt8] = [UInt8](data)

From what I understand Data is essentially "just" a [UInt8] array anyways, but if you peruse it's methods there's no obvious way to turn Data into a pure byte array. I think it is the array sequence initializer of [UInt8], and this is possible because of the Sequence Protocol.

Using the REPL

To open the swift REPL on the command line type the following,

❯ swift repl
Welcome to Apple Swift version 5.10 (swiftlang-5.10.0.13 clang-1500.3.9.4).
Type :help for assistance.
  1> import Foundation
  2> UUID()
$R0: Foundation.UUID = 8BF49C91-B76A-40F0-8674-CA5BD40A7F55
  3>

You can import Apple SDKs as well, it seems.

ctrl-D to quit.

Subscripts are pretty cool

Subscripts are essentially an abstraction over element access for collections. It might seem like overkill at first because that would 'only' abstract away accessors for enumerations/enumerable entities like Arrays, Ranges, Dictionarys, etc. But, the abstraction also allows you to implement subscripts for customer classes and structs. It also allows for creative access logic like accessing elements from a two dimensional array, which can itself be abstracted to n-dimensions.

Namespacing

In the blog post The Power of Namespacing in Swift the author mentions using enumerations to create logical namespaces.

enum Notes {
    struct Text {
        let id: UUID,
        let content: String
    }
}

I have also been using nested structs to create namespaced static library functions. This creates code in the functional paradigm, which is a preference of mine when it comes to codebase management.

struct Lib {
  static func one() {}
}

extension Lib {
  struct Namespace {
    static func two() {}
  }
}

extension Lib.Namespace {
  struct SubNamespace {
    static func three() {}
  }
}

Prefer structs over classes

From the TSPL section on comparing structs and classes:

As a general guideline, prefer structures because they’re easier to reason about, and use classes when they’re appropriate or necessary. In practice, this means most of the custom types you define will be structures and enumerations.

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