Lesson 14 of 20

6 mins read

Enums & the Option<T> Type (No Null!)

In Plain English

Rust enums are algebraic data types that can carry distinct data in each variant. Rust has no null reference; instead, the standard library provides Option<T> with variants Some(T) and None to represent presence or absence safely.

The Mental Model

"In other languages, null is like a hidden landmine in a field of flowers. In Rust, Option<T> is a sealed gift box: it is either clearly labeled Some(gift) or None (empty box), and the compiler forces you to inspect the label before opening it."

Deep Dive: How It Works

Data-Bearing Enums: enum WebEvent { Click { x: i64, y: i64 }, KeyPress(char) }

The Option<T> Enum: enum Option<T> { Some(T), None }. Included automatically in standard prelude.

Forced Safety: You cannot access inner value T without explicitly handling the None variant.

Syntax Blueprint

match maybe_value { Some(v) => println!("{}", v), None => println!("Empty") }

Forces complete handling of missing data at compile time, eliminating null pointer exceptions.

Core Rules to Remember

Zero Null Bugs: Rust completely eliminates null pointer dereferences at compile time.

Data-Bearing Enums: Variants can hold different types, structs, and payloads.

Pattern Matching: Extract Some(T) payloads safely using match or if let.

Common Beginner Traps & How to Fix Them

Mistake:Calling .unwrap() on a None value.

Why it happens: unwrap() extracts Some(v) but panics at runtime if the value is None.

How to fix: Use match, if let, or .unwrap_or(default) for safe fallbacks.

Pro Tip: Use .unwrap_or(default_value) or .map(|v| v * 2) to transform Option types concisely.

Live Interactive Example

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Option Inspection and Custom Enum

Rust 1.78 / rustc

Output Console

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How it works: Demonstrates data-bearing enums and safe Option handling with unwrap_or fallback.

Your Turn: Micro Challenge

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Micro Exercise

Unpack Option with match

Write fn find_user(id: i32) -> Option<&'static str> that returns Some("Alex") if id == 1 else None.
In main(), match find_user(1) and print "Found User: Alex".

Sandbox Output

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