Teach nested pattern matching in a new exercise

[rishitc]

From the discussion in #2127, @mo8it suggested to open a issue for tracking the inclusion of an exercise for teaching nested pattern matching.

It's been a while since that discussion, but no issue was opened to track this; hence, I opened an issue to track it.

I myself recently finished the Rustlings exercises and I came up with the below execrise which I think will help teach the concept of nested pattern matching to newcomers.

I'm sharing the source code, below:

// Author: Rishit Chaudhary
// Date: 9th November 2024

enum Color {
    Rgb(u8, u8, u8),
    Hsl(u8, u8, u8),
}

struct Position {
    x: i32,
    y: i32,
}

enum Command {
    Quit,
    Move(Position),
    Write(String, Position),
    ChangeColor(Color, Position),
}

fn main() {
    let cmds = &[
        Command::ChangeColor(Color::Hsl(0, 160, 255), Position { x: 1, y: 10 }),
        Command::ChangeColor(Color::Rgb(0, 160, 255), Position { x: 1, y: 10 }),
        Command::Move(Position { x: 1, y: 10 }),
        Command::Write("Hello".into(), Position { x: 1, y: 10 }),
        Command::Quit,
    ];

    for cmd in cmds {
        match cmd {
            Command::ChangeColor(Color::Rgb(r, g, b), Position { x, y }) => {
                println!("Change color of position ({x}, {y}) to red {r}, green {g}, and blue {b}");
            }
            Command::ChangeColor(Color::Hsl(h, s, l), Position { x, y }) => {
                println!(
                    "Change color of position ({x}, {y}) to hue {h}, saturation {s}, lightness {l}"
                )
            }
            Command::Write(text, Position { x, y }) => {
                println!("Write text \"{text}\" to position ({x}, {y}).")
            }
            Command::Move(Position { x, y }) => {
                println!("Move to position ({x}, {y}).")
            }
            Command::Quit => {
                println!("Goodbye!")
            }
        }
    }
}

Here's the Rust Playground link to the above code: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=651e559640d308b05967d2aef512bbbe

If you think this code can be added as a new exercise; I'd be happy to add the required comments explaining the exercise, and create a PR to contribute it as per the guidelines mentioned in Contributing to Rustlings.

Let me know if you have any questions or suggestions, I'd be happy to help

Thanks

[mo8it]

I will take a look at new exercises in December ;)