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Chapter 14: Option, Result, and Rust’s Error Philosophy

Prerequisites

Ch 13: Enums

You will understand

  • Why Rust has no null
  • The ? operator as early-return sugar
  • When to unwrap vs propagate errors

Reading time

30 min
+ 20 min exercises
←
Builds on Chapter 13 Option<T> and Result<T, E> are enums. Pattern matching is how you extract the success or failure value — there is no null to check. Revisit Ch 13 →
Null vs Type

Hidden Nullability vs Explicit Absence

Null NULL ordinary reference-shaped variable may secretly be invalid Option Some None caller must handle the two states explicitly
Error Flow

What `?` Expands Into

let v = parse()?; Ok(v) unwrap and continue Err(e) From::from(e) return Err(converted) happy path stays linear error path exits early
Decision Flow

Choosing How to Handle a Result or Option

Got a Result / Option? Can you handle it here? Yes match / if let No Should it propagate? Yes ? operator No Need a default? Yes unwrap_or(_else) No .unwrap() prototype / provably safe
Reach for ? first in production code — it keeps the happy path linear and makes errors the caller's problem. Use match when you need local recovery. Use .unwrap() only when you can prove the value is always present, or in tests.

Watch ? do its job twice: once on the happy path, once on the early return.

Interactive simulation (requires JavaScript): on the happy path the ? operator unwraps Ok(8080) and execution continues; on the failure path it early-returns the Err from the function, which arrives in the caller as an ordinary value that the type system forces the caller to handle.

## Step 1 - The Problem