Rust - lesson 6 | HackIndia Skills

Key point

One crate, one job

A crate is a Rust package you can reuse. Use it when it saves boring work, like parsing CLI flags, reading dates, or making coloured output.

Do not add crates because they look popular. For your internship repo, you should be able to explain why each dependency exists.

What Cargo does

Cargo reads your Cargo.toml file, downloads dependencies, builds them, and records exact versions in Cargo.lock.

For an app or CLI project, commit Cargo.lock. It helps another builder, mentor, or recruiter run the same dependency versions you used.

Your to-do

Choose a crate

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.

Search crates.io for the job you need, like CLI arguments or table output.
Check the crate page for recent versions, docs, examples, and total dependencies.
Read one short example before installing it.
Prefer a well-documented crate over a crate with clever syntax you do not understand.
Avoid adding two crates that do the same job.

0 of 5 done

Example

Add clap

clap is commonly used for parsing command-line arguments. Here is a small setup for a todo-style CLI.

This example keeps the dependency simple. It uses clap with its derive feature.

# Cargo.toml
[package]
name = "rust-todo-cli"
version = "0.1.0"
edition = "2021"

[dependencies]
clap = { version = "4.5", features = ["derive"] }

Example

Use the crate

This code lets your CLI accept an action and a task. The pattern matching is still your code. The crate only handles argument parsing.

Run it with cargo run -- add "pay hostel mess bill".

use clap::{Parser, Subcommand};

#[derive(Parser)]
#[command(name = "todo")]
#[command(about = "A small task CLI")]
struct Cli {
    #[command(subcommand)]
    command: Command,
}

#[derive(Subcommand)]
enum Command {
    Add { task: String },
    Done { id: u32 },
}

fn main() {
    let cli = Cli::parse();

    match cli.command {
        Command::Add { task } => println!("Added task: {task}"),
        Command::Done { id } => println!("Marked task #{id} as done"),
    }
}

Common mistake

Do not paste blindly

AI tools are useful for crate setup, but they often mix old syntax with new versions. Ask for the crate version you use, then check the official docs and run cargo check.

Also check that the generated code fits your project. If AI adds async, databases, or five extra crates for a simple CLI, remove the extra parts.

Tip

Keep updates controlled

When something breaks after adding a crate, read the first compiler error before changing code. Rust errors usually point to the wrong type, missing import, or missing feature flag.

Use cargo tree when your project feels heavy. It shows all dependency packages pulled in by your crates.

cargo check
cargo tree