Rust - lesson 4 | HackIndia Skills

Key point

One idea

match takes a value and maps each possible shape to an action. In a CLI, that value is often a command, a flag, or parsed input.

Use match when the next step depends on clear cases: add, list, done, invalid command.

Why it matters

Your CLI will receive messy input. A hostel expense tool may get add, split, total, or a typo like totla.

Instead of scattering if else checks across the file, put the decision in one match. It becomes easier to read during a hackathon demo and easier to change later.

Example

Match a command

This example reads the first argument after the program name. Then it maps that command to an action.

You are not building the whole app here. Focus on how the branches stay explicit.

use std::env;

fn main() {
    let args: Vec<String> = env::args().collect();

    let command = args.get(1);

    match command {
        Some(cmd) if cmd == "add" => println!("Add a new item"),
        Some(cmd) if cmd == "list" => println!("Show all items"),
        Some(cmd) if cmd == "done" => println!("Mark an item done"),
        Some(other) => println!("Unknown command: {}", other),
        None => println!("Usage: tasker add|list|done"),
    }
}

Your to-do

Read the match

Do each one yourself, then tap it to tick it off. The ticks are only a checklist for you: they are not marked or scored.

Start with the value being matched: command.
Check each arm from top to bottom.
Use Some(cmd) when the argument exists.
Use Some(other) for any command you do not recognise.
Use None when the user gave no command.

0 of 5 done

Tip

Prefer exact shapes

When possible, match on simple values. For command strings, you can convert Option into Option so your arms look cleaner.

This reduces guard clauses like if cmd == "add".

use std::env;

fn main() {
    let args: Vec<String> = env::args().collect();
    let command = args.get(1).map(String::as_str);

    match command {
        Some("add") => println!("Add a new item"),
        Some("list") => println!("Show all items"),
        Some("done") => println!("Mark an item done"),
        Some(other) => println!("Unknown command: {}", other),
        None => println!("Usage: tasker add|list|done"),
    }
}

Common mistake

Do not skip cases

Rust match must be exhaustive. That means every possible value needs a branch.

Beginners often match only add, list, and done. The compiler then complains because it also sees missing input and unknown input. Add a fallback arm instead of fighting the compiler.