Type Annotations

Part of the Fundamentals section of Coddy's Swift journey — lesson 5 of 86.

Swift can automatically figure out the type of a value. This is called type inference:

let name = "Alice"   // Swift infers this is a String
let age = 25         // Swift infers this is an Int
let price = 9.99     // Swift infers this is a Double

But you can also explicitly declare the type using a type annotation. You write a colon after the name, followed by the type:

let name: String = "Alice"
let age: Int = 25
let price: Double = 9.99
let isActive: Bool = true

Type annotations are useful when:

You want to be extra clear about what type a value is

You declare a variable without an initial value

var score: Int   // Declared but not yet assigned
score = 100      // Assigned later

Without the type annotation, Swift wouldn't know what type score should be.

Challenge

Beginner

Create four constants with explicit type annotations:

name of type String with value "Alice"
age of type Int with value 30
price of type Double with value 9.99
isOnline of type Bool with value true

Print all four values on separate lines.

Cheat sheet

Swift can automatically determine the type of a value through type inference:

let name = "Alice"   // Swift infers String
let age = 25         // Swift infers Int
let price = 9.99     // Swift infers Double

You can explicitly declare types using type annotations with a colon after the variable name:

let name: String = "Alice"
let age: Int = 25
let price: Double = 9.99
let isActive: Bool = true

Type annotations are useful when declaring a variable without an initial value:

var score: Int   // Declared but not assigned
score = 100      // Assigned later

Try it yourself

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Fundamentals

1Introduction

The Language Hello World!Comments

4Operators Part 1

Arithmetic Operators Modulo Operator Compound Assignment Recap - Simple Math Comparison Operators

7Basic IO

Print Function String Interpolation ReadLine Input Type Conversion Recap - Till 120 Recap - True or False

10Functions

Declare A Function Parameters And Arguments Return Values Argument Labels Recap - Sigma Function Recap - Validation Function Default Values

13Iterating Over Sequences

Iterating Over Elements The Enumerated Method Iterating Over Strings P1 Iterating Over Strings P2

16Final Challenges

Flat Asterisk Pyramid Pattern Finder What To Buy

2Variables

Let vs VarType AnnotationsNumbers String Boolean Naming Conventions Recap - Initialize Variables

5Operators Part 2

Logical Operators Part 1 Logical Operators Part 2 Recap - Simple Logic Logical Operators Part 3 Ternary Operator

8Bill Split Calculator

Welcome Message Getting Input

Calculating Tip And Total

Splitting The Bill

Formatted Output

11FizzBuzz with a Twist

Game Overview The FizzBuzz Function

Looping The Numbers

Adding The Twist

14Arrays Advanced

Array Slicing Part 1 Array Slicing Part 2 Sequence Operators The Contains Method