Assertions and Preconditions
Assertions and Preconditions
Assertions and Preconditions is a free Swift Academy lesson on CoddyKit — lesson 1 of 1. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Swift Academy learning path, one of 1 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Introduction
Hello,
Assertions and preconditions are the processes of checking the application at runtime.
Before running any code, it checks that certain conditions are met and this usually happens with the bool operator.
If true, the code continues. Otherwise, the code block stops running and the app becomes terminated.
cont.
Assertions are used during development to find code errors in the application. Preconditions are used to control errors during production.
We can think of them as suitable methods to provide application documentation.
We shouldn't think of these as error handling. Because if they are used and the conditions are not met, they generate errors in the application and cannot be caught.
why they are used for
They are used to fix potential errors and make it easy to debug the program.
Terminating the application immediately allows us to detect invalid statuses. Assertions are for debugging, so using them in code has no effect on productivity.
example
Let's learn the assertion mechanism by making an example.
let age = -3
assert(age >= 0, "A person's age can't be less than zero.")
// This assertion fails because -3 is not >= 0.
if age > 10 {
print("You can ride the roller-coaster or the ferris wheel.")
} else if age >= 0 {
print("You can ride the ferris wheel.")
} else {
assertionFailure("A person's age can't be less than zero.")
}precondition
Preconditions
Let's do an example with a precondition.
let index = 1
precondition(index > 0, "Index must be greater than zero.")Congratulations
Congratulations 🎉
In this lesson, we learned the concepts of Assertions and Preconditions.
See you in the next lesson 😽
Frequently asked questions
Is the “Assertions and Preconditions” lesson free?
Yes — the full text of “Assertions and Preconditions” is free to read here on the web, and the Swift Academy course includes 1 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Swift Academy course, upgrade to CoddyKit PRO.
What will I learn in “Assertions and Preconditions”?
Assertions and Preconditions You practise Swift Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Swift Academy?
No prior experience is required. Swift Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 1, so you can start here or from the beginning and move at your own pace.
How long does the “Assertions and Preconditions” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Swift Academy lesson?
Yes. Every Swift Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.