This week's exercise will introduce enums, pattern matching, if let, teach you about bringing in crates and introduce how unit testing is done in Rust.
Ensure your editor is set to format on save, and that you have the rustfmt tool installed. You can install it by running rustup component add rustfmt.
Enums are one of Rust's most powerful features. They allow us to create a type with a finite set of values.
Create an enum called Shape with three variants: Circle, Square and Rectangle, and give each variant appropriate fields
SPOILER
Circle { radius }Square { length }Rectangle { width, height }
Create a function named area that takes a Shape reference as an argument and returns the area of the shape.
Use pattern matching to determine what area to return for each of the variants.
Create a unit test named test_shape_areas (yes, in the same file) that tests whether your area function is correctly calculating the area of each of the shapes.
Use the assert_eq! macro to test the area of each shape.
Use #[test] to mark the function as a test, and cargo test to run the tests.
Bring in the rand crate to your project and create a function named random_shape that returns a randomly generated Shape.
You can install crates by either adding them to your Cargo.toml file, or by running cargo add <crate_name>.
Make sure to read the documentation for the rand crate to figure out how to generate a random number.
How do you convert a random number to a Shape? Use pattern matching with numbers!
Create a function named circle_area that takes a Shape reference as an argument and returns the area of the shape if it is a Circle, otherwise it should return 0. The return type should be f64.
Use an if let statement to determine whether the shape is a Circle and return the area if it is.
Write a test that verifies that this function works correctly.
Change the circle_area function to return an Option<f64> instead of an f64. If the shape is a Circle, return Some(area), otherwise return None.
Update the test accordingly.