Swift Comments

Why Use Comments?

Comments are lines of text in your source code that the Swift compiler completely ignores. They exist purely to help humans — including your future self — understand what a piece of code does, why it exists, or what still needs work.

Single-Line Comments

A single-line comment starts with two forward slashes `//`. Everything after `//` on that line is ignored by the compiler, whether it appears on its own line or at the end of a line of code.

// This program calculates the area of a rectangle
let width = 5
let height = 3

let area = width * height // multiply width by height
print(area) // prints 15

Multi-Line Comments

For longer explanations spanning several lines, Swift supports multi-line comments that begin with `/*` and end with `*/`. Unlike some languages, Swift allows multi-line comments to be nested inside one another.

/*
 This section handles user input validation.
 It checks that the age is a positive number
 before proceeding with registration.
*/
let age = 20
if age > 0 {
    print("Valid age")
}

/* Outer comment start
   /* Inner nested comment */
   Outer comment continues and ends here */
print("Nested comments compiled successfully")

• `//` comments out the rest of the current line
• `/* ... */` comments out everything between the markers, even across multiple lines
• Swift uniquely allows nesting `/* */` comments inside each other
• Comments are often used to temporarily disable code while debugging
• Good comments explain *why*, not just *what*, since the code already shows what it does