By the end of this lesson
Handle both Some and None without assuming a value exists.
Before you start
- Rust 1.90.0 or later, a terminal and a plain-text editor. Examples were tested with Rust 1.90.0, Edition 2024 on Linux.
- Complete lesson 15, or be comfortable explaining and running its examples.
Three words to know
- Option
- A value that is present as Some or absent as None.
- Some
- The variant containing a value.
- None
- The variant representing absence.
1. Understand the idea
Option<T> makes missing data explicit. It is an enum rather than a special null value shared by every type. Match both cases, or use a helper that reflects your intended fallback. unwrap panics on None; it is not a validation strategy for input you do not control. Think about whether absence is expected or should become an error.
2. Save, run and observe
Save this complete program as lesson.rs in a fresh practice folder. It replaces that lesson file only; keep earlier examples separately. Compile it with rustc, then run the executable. Rust source goes in the editor; rustc and cargo commands go in the terminal.
fn main() {
let values = [5, 8];
match values.get(9) {
Some(value) => println!("value={value}"),
None => println!("no item"),
}
println!("fallback={}", values.get(9).copied().unwrap_or(0));
}
What you should see · example output
no item fallback=0
rustc --edition=2024 lesson.rs -o lesson
./lesson3. Explain the result
get returns Option<&i32>. copied converts a present integer reference into a copied integer, keeping None unchanged. unwrap_or supplies zero for absence; decide whether zero could be confused with real data before using that fallback in your own program.
YOUR TURN
A small check before you continue
For a required filename, is silently falling back to an empty path a good default?
Show a suggested answer
Usually not. Treat the missing argument as a validation error and explain the expected command.
Sources and scope
Documentation and examples reviewed 2026-10-18. Provider screens, package versions and output wording can differ. Examples show expected outcomes; they are not a claim that OpenViST connected to your server or verified your setup.