RUST / CONTROL FLOW
match, if let, and exhaustive decisions
Learn how match, if let, and exhaustive decisions works in Rust, why the underlying model matters, and how to apply it in a small program without hiding important trade-offs.
What you will learn
- Explain match in Rust using the correct mental model
- Trace a focused Rust example and predict its result before execution
- Recognize a boundary case involving if let and handle it deliberately
Understanding match, if let, and exhaustive decisions
match, if let, and exhaustive decisions belongs to the practical core of Rust. Start by identifying the values or state involved and the rule that connects the input to the result.
Trace the example one operation at a time. Keep match visible in the code rather than hiding it behind an abstraction before the behavior is understood.
Test a normal case and a boundary case. The difference between the prediction and the observed result is the most useful signal for deciding what to review next.
match, if let, and exhaustive decisions is a defining part of practical Rust work. Start by identifying the data or state involved, then trace the operation that changes or interprets it. Pay attention to the rules Rust applies at this boundary, because those rules explain both the useful behavior and the common failure modes. This lesson keeps the example deliberately small, then connects it to loops, iterators, and closures so the ideas form a coherent progression rather than a list of isolated syntax facts.
Worked examples
match, if let, and exhaustive decisions example
A focused Rust example for match.
fn main() {
let message = "Hello from Rust";
println!("{message}");
}
// Lesson 6: match. Change one value and predict the result before running it.Example explained
Line 1Identify where match appears in the Rust example and name the data it operates on.
Line 2Trace the relevant Rust rule one operation at a time, recording any state, type, or control-flow change.
Line 3Change one input or boundary condition, predict the result, and compare that prediction with the documented outcome.
Important notes
Keep the first match example small enough to trace completely.
Use the normal Rust toolchain or browser workspace to compare the actual result with your prediction.
Common mistakes
Treating match as punctuation to memorize instead of a Rust behavior to reason about.
Ignoring if let until it appears in production data or a larger program.
Try it yourself
Change, predict, then run
Create a small Rust example that demonstrates match. Add a normal case and a boundary case, write down the expected result for each, then explain which Rust rule produces that result. Lesson 6 should remain small enough to trace without guessing.
Open Rust workspaceCheck your understanding
What is the best first step when working with match?
- Identify the data and predict the result
- Add more abstraction immediately
- Ignore boundary cases
- Memorize punctuation only
Show answer
A clear input, operation, and predicted result create a testable mental model.