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Comments

Comments are programmer readable instructions to help explain things about your code. The compiler ignores them.

Types of Comments in Rust

Rust has two types of comments that are commonly used:

Line Comments //

The comments followed by a double forward slash, //, are known as line comments.

This is the most recommended style of comment for commenting a single line.

// Writing a Rust program
fn main() {
    //The line comment is the recommended comment style
    println!("This is a line comment!"); // print hello World to the screen
}

Block Comments /*...*/

Text enclosed within /*...*/ is known as a block comment.

This is used for temporarily disabling a large chunk of code.

Doc Comments

The comments followed by /// or //! are known as doc comments. Let’s see the difference between the two sets of doc comments.

Outer Doc Comments ///

Outer doc comments are written outside the block of code.

This type of comment supports markdown notation. This is used to generate docs referring to the following item.

Inner Doc Comments //!

Inner doc comments are written inside the block of code.

This comment style is used to generate docs referring to the item within a block of code.

/// This is a Doc comment outside the function
/// Generate docs for the following item.
/// This shows my code outside a module or a function
fn main() {
    //! This a doc comment that is inside the function   
    //! This comment shows my code inside a module or a function  
    //! Generate docs for the enclosing item
    println!("{} can support {} notation","Doc comment","markdown");
}

Quiz

Test your understanding of comments in Rust!

  1. Which type of comment is this? // a) Line b) Doc

  2. Which comment supports markdown notation? a) Line comment b) Doc comment