Option and Result Types

No Null, No Exceptions

Rust doesn't have null or exceptions. Instead it uses two enums:

Option<T> — Maybe a Value

Rust

enum Option<T> {
    Some(T),
    None,
}

Use when a value might not exist:

Rust

fn find_user(id: u64) -> Option<String> {
    if id == 1 {
        Some(String::from("Alice"))
    } else {
        None
    }
}

match find_user(1) {
    Some(name) => println!("Found: {name}"),
    None => println!("Not found"),
}

Result<T, E> — Success or Failure

Rust

enum Result<T, E> {
    Ok(T),
    Err(E),
}

Use when an operation can fail:

Rust

use std::num::ParseIntError;

fn parse_age(input: &str) -> Result<u8, ParseIntError> {
    input.parse::<u8>()
}

The ? Operator

Propagate errors without verbose match blocks:

Rust

fn get_user_age(input: &str) -> Result<u8, ParseIntError> {
    let age = input.parse::<u8>()?; // returns Err early if parse fails
    Ok(age)
}

Useful Combinators

Rust

// Option
let name = find_user(1).unwrap_or(String::from("Unknown"));
let upper = find_user(1).map(|n| n.to_uppercase());

// Result
let age = parse_age("25").unwrap_or(0);
let doubled = parse_age("25").map(|a| a * 2);

Why This Matters for Solana

Anchor programs return Result<()>. Every instruction handler uses ? to propagate errors. Understanding this pattern is essential.

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Module 1: Result and Option

Module 2: Custom Errors in Practice

Option and Result Types

No Null, No Exceptions

Option<T> — Maybe a Value

Result<T, E> — Success or Failure

The ? Operator

Useful Combinators

Why This Matters for Solana