Rust for C-Programmers

10.9 Enums as the Basis for Option and Result

Rust’s core Option<T> and Result<T, E> types are prime examples of the power of enums.

10.9.1 The Option<T> Enum: Handling Absence

Replaces NULL safely, encoding potential absence.

#![allow(unused)]
fn main() {
enum Option<T> {
    Some(T), // Represents presence of a value of type T
    None,    // Represents absence of a value
}
}

• No Null Errors: Forces explicit handling of None via pattern matching or methods.
• Type Safety: Option<String> is distinct from String. Requires explicit unwrapping.

Covered in detail in Chapter 14.

10.9.2 The Result<T, E> Enum: Handling Errors

Standard way to represent operations that can succeed (Ok) or fail (Err).

#![allow(unused)]
fn main() {
enum Result<T, E> {
    Ok(T),  // Represents success, containing a value T
    Err(E), // Represents failure, containing an error E
}
}

• Explicit Errors: Type system signals potential failure; encourages handling both Ok and Err.
• Clear Paths: Separates success value (T) from error value (E).

Covered in detail in Chapter 15.