Structs and enums · Coding Class

Basics · Build a program← Read the Learn chapter

Apply the chapter in three steps: an exercise, a program project, and a debugging task. Implement first, then consult the hints and completion criteria. Use a separate file or working directory for each task.

1. Exercise · Classify states

Declare enum Status { Pending, Done, Failed(String) } and write a function formatting each state.

Completion: Pending formats as pending, Done as done, and Failed(“disk”) as failed: disk.

Hint: Make every match branch return String.

2. Build a program · Build a task card

Define Task with String title and Bool done, plus a label method including the state. Print incomplete and complete cards titled read.

Completion: Output is todo: read, done: read. Make the variable mutable if changing its state.

Hint: Use the chapter’s &self method call form; there is no need to create explicit references.

3. Debug · Fix an incomplete match

Check the code below and handle the missing state explicitly. Name both variants instead of using _.

Start with this deliberately broken program.

class_match.xen

enum State { Ready, Waiting }
fn label(state: State) -> String {
    return match state { State.Ready => "ready", };
}
fn main() { println(label(State.Waiting)); }

xen check class_match.xen

Diagnostic excerpt:

class_match.stderr

non-exhaustive match; missing Waiting

Completion: Ready returns ready, Waiting returns waiting, and checking succeeds.

Hint: Every enum variant must be covered.

Verify and record

Use xen check file.xen followed by xen run file.xen for ordinary programs; use xen test file.xen for test-only files. Record the original error, its cause, and the corrected result, then rerun every input in the completion criteria.