In Swift an optional is a type made using an enum with two scenarios; none and some. "None" can also be represented by a special keyword "nil". "Some" has a variable attached to it. If we want to retrieve the variable then we can extract it through something called optional binding (although other options exist also).
enum Optional<T> {
case some(T)
case none
}
let containsAValue: Int? = 100
let noValue: Int? = nil
Download Xcode Playground - Topic: Optionals
Xcode Playground - Optionals Workbook
Download our Optionals workbook. Opens in Xcode. The accompanying video can be found after enrolling in the 3-day course. here.
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Optionals are explained in our 3-day online course.
Below is a rough format of how optionals are declared, checked to see if they contain a value and also extracting that value.
// 1. How to use the Optional type
let optional: Int? = nil
// 2. How to check if the variable is empty
if optional == nil {
}
// 3. How to check if the variable contains a value
if optional != nil {
}
// 4. How to extract an existing value
if let value = optional {
print("Value: \(value)")
}
Optional Binding
Optional binding is the best method of checking to know if a value is contained within the optional as well as actually extracting it if one exists.
The if statement performs the comparison whilst also extracting the associated value and placing the contents into a newly created variable made available to the code within the if statement.
// 1. How to unwrap stored values
let exam1: Int? = 55
if let exam1Score = exam1 {
print("Exam 1: \(exam1Score)")
}
The Problem Optionals Solve
In code we often do not have a value and at some point in the future we may populate this field. Numerous reasons exist for this, such as if a user has a middle name, or extra data has not been downloaded yet.
In the example below, we can see that an empty string is used to represent the absence of a value. However, this is not the absence of a value and is in fact a value, but empty. This empty string is a valid piece of data and would be foolish to introduce a "marker" to signal that in this event we can assume the data is missing rather than being empty (sometimes it's valid for the data to be empty).
Nil provides us with a Swift-supplied signal that our data is missing. When we have actual data (whether its empty or not) we can extract it and use it knowing that what ever it is, it is the fully downloaded and ready information.
// 1. The problem optionals solve
let stringValue: String = ""
if stringValue.count > 0 {
print("Value: \(stringValue)")
} else {
print("No value found")
}
Not built with A.I. A human with decades of experience wrote this article. It's designed to help you and provide some real-life guidance to start a career in the tech industry with some solid success, lots of growth and being great at what you do.
What Other Topics Do I need to Learn?
Foundational types, control flow, optionals, functions, closures, classes, structs, enums, value types, reference types, ARC (Automatic Reference Counting), extensions, protocols, concurrency, error handling and generics.
Below is the full list, available to download in markdown language.
Download
The recommended topics to study are those that each iOS Developer would be required or expected to know in order to pass an interview for a junior, mid-level or even a senior role.
Swift Study Guide
3DaysOfSwift.com | Online Swift Course
Beginner Topics
Topic 1: The Basics & Foundational Types
https://docs.swift.org/swift-book/documentation/the-swift-programming-language/thebasics
Topic 2: Control Flow
https://docs.swift.org/swift-book/documentation/the-swift-programming-language/controlflow
Topic 3: Optionals
https://docs.swift.org/swift-book/documentation/the-swift-programming-language/optionalchaining
Topic 4: Functions
https://docs.swift.org/swift-book/documentation/the-swift-programming-language/functions
Closures
https://docs.swift.org/swift-book/documentation/the-swift-programming-language/closures
Topic 5: Classes
https://docs.swift.org/swift-book/documentation/the-swift-programming-language/classesandstructures
Topic 6: Structs
https://docs.swift.org/swift-book/documentation/the-swift-programming-language/classesandstructures
Topic 7: Enums
https://docs.swift.org/swift-book/documentation/the-swift-programming-language/enumerations
Topic 8: Value Types
Reference Types
Topic 9: ARC (Automatic Reference Counting)
Mid-level Topics
Topic 10: Extensions
https://docs.swift.org/swift-book/documentation/the-swift-programming-language/extensions
Topic 11: Protocols
https://docs.swift.org/swift-book/documentation/the-swift-programming-language/protocols
Topic 12: Concurrency
https://docs.swift.org/swift-book/documentation/the-swift-programming-language/concurrency
Topic 13: Error Handling
https://docs.swift.org/swift-book/documentation/the-swift-programming-language/errorhandling
Topic 14: Generics
https://docs.swift.org/swift-book/documentation/the-swift-programming-language/generics
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Where to Learn Swift 3DaysOfSwift.com
The website starts each students learning journey with a free 3 lesson preview. All you have to do is to sign up and start learning Swift free of charge. The 4th lesson will be provided by subscribing to a monthly plan which unlocks all of the online programs including the Developers Toolkit (Language reference guides and downloadable code examples). After completing the 3-day course each student will continue to enrol in the numbered programs displayed in our members centre. The 3rd program will start the students collection of the Developers Toolkit; The Official Swift Book written by Apple, a professionally written Xcode project and The Swift Cheatsheet (language reference guide).
How to Enrol
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