Cargo — Bundler + Rake Combined Into One

Mapping table

Cargo.toml — Ruby's Gemfile

[package]
name = "myproject"
version = "0.1.0"
edition = "2021"

[dependencies]
serde = { version = "1.0", features = ["derive"] }
reqwest = { version = "0.11", features = ["json"] }
tokio = { version = "1", features = ["full"] }

Difference from Gemfile: TOML format, and features let you selectively enable crate functionality. Ruby gems don't have this concept.

cargo commands — frequently used

cargo new myproject     # new project (creates Gemfile + directory structure)
cargo build             # compile (bundle install + build)
cargo run               # build + run
cargo test              # run tests
cargo check             # type check only (faster than build)
cargo add serde         # add dependency (like bundle add serde)
cargo doc --open        # generate docs + open in browser

cargo check does type checking without building. Much faster. Useful for checking errors while coding.

Project structure

myproject/
├── Cargo.toml    # dependencies + metadata
├── Cargo.lock    # version lock (should commit)
└── src/
    ├── main.rs   # executable entry point
    └── lib.rs    # library entry point (optional)

Like Ruby puts code in lib/, Rust uses src/.

Testing — written in the same file

Ruby separates tests in spec/. Rust can put tests in the same file.

// src/lib.rs
fn add(a: i32, b: i32) -> i32 {
    a + b
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_add() {
        assert_eq!(add(2, 3), 5);
    }
}

#[cfg(test)] compiles only in test builds. Run with cargo test.

Release build

cargo build --release  # optimized binary
# → target/release/myproject

Result is a single binary. No interpreter needed like Ruby. Copy one file to the server and you're done.