Result and Option

Last reviewed May 28, 2026 Content v20260528

Track mode: server_compiled
Means: Compiled runner
Reading: ~1 min
Level: intermediate

This lesson

This lesson teaches Result and Option: the syntax, APIs, and habits you need before advancing in Rust.

Result and Option replace exceptions—explicit error paths are idiomatic and required in production Rust.

You will apply Result and Option in contexts like: Infrastructure CLIs, proxies, game engines, blockchain nodes, and latency-sensitive backends.

Write Rust with fn main(), click Run on server—the dev runner compiles main.rs with rustc and runs the binary; fix borrow errors from stderr (requires Rust toolchain; LEARNING_RUNNER_ENABLED=true).

When you can explain the previous lesson's ideas without copying starter code.

Option<T> models absence (None) or presence (Some). Result<T, E> models success (Ok) or failure (Err)—Rust's alternative to null and exceptions.

Option

fn maybe() -> Option<i32> { Some(42) }

Result

fn parse_n(s: &str) -> Result<i32, std::num::ParseIntError> {
    s.parse()
}

Important interview questions and answers

Q: Option vs null?
A: Compiler forces handling None—no silent null dereference.

Self-check

What variants does Result have?
When use Option vs Result?

Pitfall: Do not unwrap() in production paths—handle None and Err or propagate with ?.

Interview prep

Option vs Result?: Option models optional values (Some/None); Result models recoverable errors (Ok/Err).

Interview tip Lesson completion confidence

Can you explain this lesson in 30 seconds without reading notes?

Self-reflection (saved on this device)

Not saved yet.

Playground

Runs on the configured server runner (dev: npm run runner with LEARNING_RUNNER_ENABLED=true). Output appears below the editor.

Code runner not available

Server runner is disabled. Set LEARNING_RUNNER_ENABLED=true and LEARNING_RUNNER_URL in .env (see .env.example).

Check yourself

Multiple choice — immediate feedback.

Discussion

Past discussion is visible to everyone. Only logged-in users can post comments and replies.

Starter discussion topics

unwrap danger?
? operator?

No discussion yet. Be the first to ask a question.