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<!-- Copyright 2023 Google LLC SPDX-License-Identifier: CC-BY-4.0 -->

Solution

rust,editable
# // Copyright 2023 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
{{#include exercise.rs:solution}}
  • Enums with Data: Rust enum variants can carry data. CarArrived(Floor) carries an integer, and ButtonPressed(Button) carries a nested Button enum. This allows Event to represent a rich set of states in a type-safe way.
  • Type Aliases: type Floor = i32 gives a semantic name to i32. This improves readability, but Floor is still just an i32 to the compiler.
  • #[derive(Debug)]: We use this attribute to automatically generate code to format the enums for printing with {:?}. Without this, we would have to manually implement the fmt::Debug trait.
  • Nested Enums: The Button enum is nested inside Event::ButtonPressed. This hierarchical structure is common in Rust for modeling complex domains.
<details>
  • Note that Event::CarDoorOpened is a "unit variant" (it carries no data), while Event::CarArrived is a "tuple variant".
  • You might discuss why Button is a separate enum rather than just having LobbyCallButtonPressed and CarFloorButtonPressed variants on Event. Both are valid, but grouping related concepts (like buttons) can make the code cleaner.
</details>