Some best practices for designing and coding Swift classes

My original article — “Best Practices for Building Swift Classes” — was published on appcoda.com.

Follow along as I write this tutorial’s Swift code in a playground! Download from GitHub.

In this tutorial, I’m going to show you some best practices that will help you design and implement classes (reference types) and then safely leverage reference semantics in Swift. Protocol-oriented programming (POP) and value semantics are all the rage now, but a promising new technology doesn’t mean you should throw all your classes away. Why not add some simple constructs to your classes like copy initializers, default initializers, designated initializers, failable initializers, deinitializers, and conformance to the Equatable protocol? To get real about my sample code, I’ll adopt these constructs in some classes and show you my best practices working in real life for drawing in your iOS app interfaces.

I’ll walk through the process of creating several protocols, creating classes that adopt those protocols, implement inheritance in these classes, and use instances of the classes (objects), all to illustrate my best practices — and to show some of the extra steps you may have to go through when working with classes.

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Building a generic doubly linked list using protocol-oriented Swift 4

My original article — “Protocol-oriented Data Structures in Swift 4: A Generic Doubly Linked List” — was published on appcoda.com.

Follow along with this tutorial! Download the Swift 4 code from GitHub.

Let’s talk about creating a list on steroids, i.e., a generic doubly linked list in Swift. For our purposes here, a list is a software receptacle that contains related data that we’re interested in inspecting, organizing, manipulating, etc. A doubly linked list stores a list of “nodes.” Each node contains data, knows about the preceding node in the list, and knows about the following node in the list. We’ll talk about adding nodes to the list, removing nodes from the list, displaying information stored in nodes in the list, and traversing the list. I’ve used the term generic because you’ll see that I can store store pretty much every built-in or custom Swift type in my linked list, like Double, UINavigationController, Int, CGFloat, UIView, CGAffineTransform… You can even store a collection of instances of a custom class or struct in my list (see section “Storing custom types” below). Most importantly, I’ll show you how to move towards generic programming, also known as generics, parametric polymorphism, templates, or parameterized types, where, when possible, we can write code that applies to many types, and thus reduces code redundancy.

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Self versus self in Swift 4 – capital “S” and lowercase “s”

RELATED: Find out how to make a copy of a class instance (object) using a C++-like copy constructor — a copy initializer in Swift.

Those of you who’ve used Objective-C and Swift for any meaningful length of time must be familiar with the self property of structs and classes. I’m not sure how many are aware of the Self “type” (sometimes called a “requirement”). I would be very interested in knowing how many understand the difference between self and Self. I’m talking about self with lower-case “s,” which I’ll call “small self” herein. It’s pretty well documented. Similarly, Self with an upper-case “S,” is what I’ll call “tall self” herein. It’s not very well documented.

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Class copy constructors in Swift 4 for defensive copying

Swift tutorials by iosbrain.com Notice that Swift almost seems to frown on making a copy of a reference type, i.e., a copy of an instance of a class, or, as some would rather put it, getting a copy of an object. I’m not talking about getting another reference to a class, I’m talking about getting an entire, separate copy of a class instance. This frowning on class copying is not an accident. Swift’s language architects want the syntax and semantics of the language to be crystal clear. They want developers to be confident that reference types and value types will both have 1) distinct and obvious meanings and that both types will 2) behave consistently. But still, why not be able to safely make a copy of a class instance? I’ll show you how in this tutorial by borrowing the copy constructor concept from C++. In Swift, we’d call this a “copy initializer.” (NOTE: Yeah, yeah, yeah, I know about NSCopying in Cocoa and Objective-C.)

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Two Structural Design Patterns in Swift: Facade and Adapter

Swift tutorials by iosbrain.com My original article — “Design Patterns in Swift #3: Facade and Adapter” — was published on appcoda.com.

This tutorial is the third installment in my series on design patterns. I started with a tutorial examining two examples of patterns in the “creational” category: factory method and singleton. I then discussed two examples of patterns in the “behavioral” category: observer and memento. In this tutorial, I’ll explain two examples of patterns in the “structural” category: facade and adapter. I urge you to review my first two posts mentioned above so you can familiarize yourself with the concept of software design patterns. Beyond a brief reminder today of what constitutes a design pattern, I’m not going to regurgitate all the definitions again. All the information you need to get up to speed is in my first to tutorials, here and here.

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How drawing works in an Xcode playground

How many of you use freeform drawing in Xcode playgrounds? How many of you understand how drawing in playgrounds work? Xcode playgrounds can serve as great tools for prototyping your in-development apps, whether it be experimenting with algorithms or toying with ideas for app user interfaces. Granted that drawing in playgrounds is not that well documented. So the subject of this tutorial is how drawing in Xcode playgrounds works and a good number of pointers to help you start drawing in playgrounds. Here’s an example of what I’m talking about:

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Fix for prohibitory symbol (do not enter, stop sign) when booting into or updating macOS Mojave 10.14 beta

Over the last week, I encountered the dreaded Apple “prohibitory symbol” — do not enter sign or stop sign — twice: once when just booting into macOS Mojave 10.14 beta 4 and again when updating to macOS Mojave 10.14 beta 8. Here’s what my MacBook Pro’s screen showed me:

The is one of the symbols that users of Apple products running macOS rightfully fear. Of course, we’re talking about products like the Mac Pro, Mac mini, iMac, MacBook, MacBook Air, and MacBook Pro.

When you see the prohibitory symbol, please don’t panic. Please don’t go through any lengthy reinstalls or plunge down the troubleshooting rabbit hole before you hear me out. Apple says you should “try reinstalling macOS using macOS recovery.” Another Apple support page suggests that you “revert to a previous version of macOS if you experience trouble after installing an update” (using Time Machine). Several Apple forums advise booting from a recovery hard drive, reinstalling macOS, repairing your hard drive with Disk Utility… These are all valid solutions… ones you should only use after trying something simple first.

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Swift 4.2 improvements? Member/dot syntax for subscripts. Trying it out in a protocol-oriented, generic linked list.

The code shown herein will only compile and link in Xcode 10 beta and run on iOS 12 beta and/or OS X 10.14 beta.

While working on a Swift protocol-oriented and generic linked list, I got to thinking about Apple’s “improvements” to version 4.2 of their flagship language. Since a linked list is a list, I thought, “Why not add a subscript to my linked list to facilitate finding specific nodes in my list?” I did that in Swift 4.1 and got what most developers would’ve expected, e.g., used linkedList["node4"] to get the node in the list associated with the keyword “node4.” With Swift 4.2, I can use the controversial new @dynamicMemberLookup language attribute and implement dot/member notation, like linkedList.node4 to get that same node in the list associated with “node4.” Big improvement, huh? Well, maybe. We’ll talk about how this new and improved subscript is more than just about syntactic sugar, but that the “driving motivation for this feature is to improve interoperability with inherently dynamic languages like Python, Javascript, Ruby and others.” Note that all code shown in this tutorial was written in two Xcode 10 beta playgrounds.

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Xcode 9 playground error: No such module ‘UIKit’ (or ‘AppKit’)

While creating a new Xcode playground on my MacBook Pro today, I got the most bizarre error message: “No such module ‘UIKit'”. I was using Xcode Version 9.2 (9C40b). Yes, I know there are more recent versions, but I haven’t had the need to upgrade my MacBook Pro. Parenthetically, I do have Xcode 9.4.1 (9F2000) and Xcode 10 beta 6 (10L232m) loaded on my main development machine. I’ll share the solution to this problem with you in the hopes that you, like me, will learn something new about Xcode today.

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Swift 4.2 improvements: #warning and #error compiler directives

The code shown herein will only compile and link in Xcode 10 beta and run on iOS 12 beta and/or OS X 10.14 beta.

We’re in the middle of Apple’s annual product upgrade cycle and this article is the second in a series of tutorials, started last week, meant to highlight the most important new features of Swift 4.2. Today, we’ll look at two two new Swift 4.2 features, the #warning and #error compiler directives.

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