Module 33: Macros

Practice Tasks

Complete these tasks to reinforce what you learned in this module.

Task 1: Simple expression macro

Define a macro double! that takes one expression and expands to that expression added to itself (e.g. double!(5) becomes 5 + 5). In main, print the result of double!(10).

Expected Output:

Hint: The macro should match one expression and expand to that expression used twice (e.g. added to itself). Use $e:expr in the pattern and $e in the expansion.

Starter Code:

task.rs

// Task 1: double! macro. See tasks/TASKS.md.

fn main() {
    todo!("macro_rules! double, print double!(10)");
}

Task 2: Macro with repetition

Define a macro sum! that takes zero or more expressions separated by commas and expands to their sum. For example sum!(1, 2, 3) becomes 1 + 2 + 3. Use $( $e:expr ),* and repetition in the expansion: $( $e )+ with a single + between them (you can use a trick: expand to 0 $( + $e )*).

Expected Output:

With `sum!(1, 2, 3, 4)`, running `cargo run -p course_33_macros --bin task_02` prints:

Hint: Use repetition: match zero or more expressions separated by commas, then in the expansion repeat + $e for each. Starting from 0 and adding each term gives the sum. The theory explains $( ... )*.

Starter Code:

task.rs

// Task 2: sum! macro. See tasks/TASKS.md.

fn main() {
    todo!("macro_rules! sum with repetition, print sum!(1,2,3,4)");
}