Comments

Document your code with // and /* */ comments.

Comments

Rust has three kinds of comments: // single line, /* ... */ multi-line, and /// doc comments. Doc comments become HTML documentation with cargo doc, and the code examples inside them run as tests.

/// İki sayıyı toplar.
/// ```
/// assert_eq!(topla(2, 3), 5);
/// ```
fn topla(a: i32, b: i32) -> i32 {
    a + b // the result is returned as an expression
}

Good comments

A good comment explains why the code does something, not what it does. The code itself should already say what it does through readable names. //! at the top of a file or crate documents the whole module.

// Bad: increment i
i += 1;

// Good: skip the header line
i += 1;

Exercise Documented function

Write a fn kare(n: i32) -> i32 function documented with ///, and in main call println!("{}", kare(9)); under a // comment.

Show example solution

/// Sayının karesini döndürür.
fn kare(n: i32) -> i32 {
    n * n
}

fn main() {
    // 9'un karesini yazdır
    println!("{}", kare(9));
}

Test yourself

What happens to code examples in <code>///</code> comments?
- Only the IDE shows them
- They run as tests with cargo test
- They are ignored
- They cause a compile error
Show answer

They run as tests with cargo test — This feature, called doc tests, guarantees that the examples in the documentation stay current and correct.

Doc comment

____ Dairenin alanını hesaplar.
fn alan(r: f64) -> f64 { 3.14 * r * r }

Show answer

/// Dairenin alanını hesaplar.
fn alan(r: f64) -> f64 { 3.14 * r * r }

Comment kind

//

Single line
/* */

Multi-line
///

Item documentation
//!

Module documentation

Next lesson: Summary - Rust basics

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies