Swift design patterns – which are the most popular?

Finding universal solutions to problems, and templates for widespread use in such cases is probably the domain of every field. Hence, a design pattern is a term commonly known to mobile application developers and software developers in general. Let’s narrow down these considerations to our today’s hero, Swift. It’s a programming language developed by Apple mainly for its products. First introduced in 2014, Swift is a strong successor to the language previously used by Apple, Objective-C. 

When creating software in Swift, as with other object-oriented languages, developers have a wide variety of design patterns at their disposal. As intended, they enable the creation of highly functional and secure applications, while simplifying the code development process. Before we discuss a few of them and their peculiarities, let’s start by explaining what design patterns are, where they came from, and what they are characterized by.

What are the design patterns?

Design patterns are universal, proven in practice solutions to repetitive, frequently occurring design problems. They are used in projects using object-oriented programming and are a description/template for a solution, not its implementation. They show relationships and dependencies between classes and objects and facilitate the creation, modification, and maintenance of the source code. Design patterns introduce some code standardization and increase its intelligibility, reliability, and efficiency. 

The idea was transferred directly from architecture, where it did not catch on. In 1987, Kent Beck and Ward Cunningham began experimenting with the idea of applying patterns to programming and presented their results at the OOPSLA conference this year. In the following years, they continued working on them. Design patterns gained popularity in computer science after publishing in 1994 by the so-called “Gang of Four” from Design Patterns: Elements of Reusable Object-Oriented Software. Design patterns can accelerate the development process by providing tested, proven solutions to common problems and positively impact efficiency.

Design patterns can also be classified. As we only focus on Swift now, let’s see what types we can distinguish in this language:

1. Creational 

These design patterns deal with object creation mechanisms by trying to create objects as appropriate to the situation. Creational patterns address potential design flaws and increased complexity by controlling the creation of this object in a specific way. They are based on two dominant ideas. One of them is encapsulating the knowledge of what specific classes the system is using, and the second one is about hiding how instances of those specific classes are created and combined. Various types of creational design patterns are available in Swift, such as Factory, Abstract, Singleton, Builder, etc.

2. Structural 

Structural Design Patterns are patterns that ease the application design process by finding an easy way to implement relationships between elements. They explain how to combine objects and classes into larger structures while maintaining the flexibility and efficiency of these structures. Among them, you can list Facade, Adapter, MVC, etc.

3. Behavioural 

Behavioural design patterns identify common communication patterns between objects, thus increasing their flexibility. They deal with algorithms and assigning responsibilities between objects. Popular patterns of this type in Swift include Template Method, Observer and Memento.

Most popular design patterns in Swift

Swift’s (or iOS) design patterns are the same as in other languages and are used in standard use cases. Most of them were introduced a few decades ago at the time of the greatest development of programming and laying the foundations for today’s good practices. Let’s focus on a few of the patterns to understand the principles of their operation and the benefits they bring.

MVC Pattern

The MVC pattern, or Model View Controller, is one of the most frequently used design patterns and recommended by Apple for creating an iOS application structure. As the name suggests, MVC consists of three main components:

• Model – the central component of the pattern. It is the application’s dynamic data structure, independent of the user interface. It directly manages the data, logic and rules of the application;
• View – describes how to display a certain part of the model within the user interface. It can consist of sub-views for smaller portions of the interface;
• Controller – accepts input from the user and reacts to his actions, managing model updates and refreshing views. It is the element that connects the Model and View layers. The Controller should not know the specific implementation of the View it will be working with.
  

Model-View-Controller is a fundamental concept in iOS programming. Many iOS platforms, such as UIKit, use the MVC pattern to structure data flow and messaging. Its advantage is the clear separation of concerns. Each pattern layer is responsible for a specific aspect of the application. Thanks to MVC, the code is not chaotic but has a specific structure. The pattern makes it concise and readable.

Facade Pattern

A facade pattern is a software design pattern that provides a simple interface to a library, framework, or class set. Like a facade in architecture from which, as we mentioned, patterns are derived, a facade is an object that serves as a front interface masking more complex underlying or structural code.

The facade is a model that aims to standardize and facilitate access to a complex system. Its structure consists of the following elements:

• Client – a certain code interested in using a complex system;
• A complex system – It consists of many subsystems and elements. We want to facilitate access to it;
• Facade – a class that has references to system components and provides convenient access to these specific parts of the subsystem functionality.

The client communicates with the system through a facade that performs the necessary operations on a complex system for him. It is possible to use a pattern to divide the system into layers, where the facades are used to simplify and standardize communication and give the client direct access to the system.

The use of this pattern is recommended when you can provide a simpler interface and simplify the use of its functionalities. The Facade pattern hides the complexity of the system from the client, which results from its construction and ensures its correct operation. It is also a good solution for systems that have many dependent subsystems as it separates the details of their implementation and reduces dependencies. As a result, the code is easier to understand, use, and maintain.

Memento Pattern

As you may have noticed by now, the pattern names are not accidental. A memento is a pattern that provides the ability to save and restore an object to a previous state without revealing implementation details.

It is implemented using three objects:

• Originator – some object that has an internal state. It can create snapshots of its state and can also restore its state from snapshots when needed;
• Caretaker – requests a save from the initiator and in response, receives a memento. It is responsible for perpetuating the memento and then delivering it back to the creator to restore it to its state. A caretaker can keep track of the originator’s history by storing a stack of mementoes;
• Memento – a value object that acts as a snapshot of the seed state. The memento itself is an opaque object that the caretaker cannot, or should not change. It is common practice to make a memento invariable and pass its data only once, via the constructor.

The Memento Design Pattern is one of the fundamental, well-known GoF design patterns. Memento helps to solve the problem of encapsulating an object whose data structure is hidden inside the object and cannot be accessed from outside. It makes the Originator object itself responsible for writing its internal state to the Memento and restoring it to a previous state. Only the Originator that created Memento has access to it. This way, the Caretaker can request a Memento from the Originator to save the creator’s internal state and pass it back to the creator to restore it to the previous state. This allows to save and restore the internal state of the initiator without breaking its encapsulation.

Builder Swift Pattern

Another well-known design pattern in the Swift world. Builder is a creational design pattern whose purpose is to separate the way objects are created from their representation. In other words, the process of creating an object is broken down into several smaller steps, and each of these steps can be implemented in many ways. Thanks to this solution, it is possible to create different representations of objects in the same construction process. The method of creating objects is closed in separate objects called Concrete Builders. 

By default, a pattern consists of two basic objects. The first one is marked as the Builder – its purpose is to provide an interface for creating objects called products. A second object is an object marked as a Concrete Builder, and its purpose is to create specific representations of products using the implemented Builder interface. The Concrete Builder contains procedures responsible for the construction and initialization of the facility. The pattern structure is completed by the Director’s facility, which orders the construction of products through the Builder’s facility, ensuring that the construction process is carried out in the right order.

It is usually used for the construction of complex objects, the configuration, and initialization of which is a multi-stage process. It differs from the other creational patterns in that it focuses on the way of creating objects representing products. It creates a small part of a complicated product each time it is invoked while controlling the state of the work done. The customer receives the product at the end of its work, not immediately. The advantages of using the pattern are high scalability through the simplified addition of new representations of objects, the large possibility of differentiating internal class structures, and better ability to control how the object is created in individual procedures.

Decorator Pattern

The Decorator pattern dynamically adds behavior and responsibilities to an object without affecting the behavior of other objects in the same class. A pattern is useful for adhering to the Single Responsibility Principle as it allows functionality to be broken down into classes with unique areas of interest. The decorator pattern wraps the original class into a new “decorator” class. Typically you pass the original object as a parameter to the decorator constructor, the decorator methods call the original object’s methods, and additionally implement the new function.

Decorators are an alternative to inheritance. Inheritance extends class behaviour at compile time, unlike decorators which extend classes at runtime. Since most object-oriented programming languages cannot create new classes while the program is running, and you usually cannot predict all combinations of class extensions in advance, you would have to create a new class for each combination. Decorators are objects that are created at runtime and can be combined into various combinations directly using.

In Swift, there are two very common implementations of this pattern: Extensions and Delegation. The extension is used to add new behaviors and functions for predefined classes, structures, and enumerations without having to subclass. You can add behavior to UIView, UIImage, and other Cocoa classes with extensions. Delegation is the mechanism by which one object transfers responsibility to another object if that other object agrees. The consequences of using Decorator are greater flexibility than in the case of inheritance and avoiding classes overloaded with functions at high levels of the hierarchy.

What are the advantages of Design Patterns Swift for iOS App Development?

Design patterns were created with ease of coding in mind, that’s a fact. They are reusable solutions for common problems and designed to help you write code that is easy to understand and reusable. They also help in creating loosely coupled code, so you can change or replace components in your code without much hassle. Let’s briefly discuss their advantages.

Code unification

Design patterns provide common solutions that have been tested for bugs and software flaws. As a result, developers make fewer mistakes when using patterns when designing an application architecture.

Proven, tested solutions.

Design patterns already provide the best solution and tell you how to implement them without having to spend time looking for a way to solve a given programming problem. So they’re a way to speed up the app development process. It is worth noting, however, that they are not the answer to every problem, so the decision to implement them depends on the developer and his experience.

Common nomenclature

The names of the patterns, and thus their characteristics and use cases, are commonly known to programmers. There is no need for an advanced explanation of the selected solution. It is enough to just say what pattern you use. 

Summary 

Design patterns are toolkits that iOS developers and any other technology users apply in their everyday work. They define a common language that helps a team communicate more efficiently. Undoubtedly, they can systematize the software development process and give many benefits if used well.

Read more about Swift in our related articles:

• React Native vs Swift – Which is better? Which to choose?