how-to-use-an-enum-in-a-rust-hashmap.md

How to use an enum in a Rust HashMap?

// plain

Enums can be used as keys in a Rust HashMap. To do this, the enum must implement the Eq and Hash traits.

Example code

use std::collections::HashMap;

#[derive(Eq, Hash, PartialEq)]
enum Color {
    Red,
    Blue,
    Green,
}

fn main() {
    let mut colors = HashMap::new();
    colors.insert(Color::Red, "red");
    colors.insert(Color::Blue, "blue");
    colors.insert(Color::Green, "green");

    println!("{:?}", colors);
}

Output example

{Color::Red: "red", Color::Blue: "blue", Color::Green: "green"}

Code explanation

1. #[derive(Eq, Hash, PartialEq)]: This line is used to derive the Eq, Hash, and PartialEq traits for the Color enum. This is necessary for the enum to be used as a key in a HashMap.

2. let mut colors = HashMap::new();: This line creates a new empty HashMap.

3. colors.insert(Color::Red, "red");: This line inserts a key-value pair into the HashMap. The key is the Color::Red enum variant, and the value is the string "red".

Helpful links

• Rust HashMap documentation
• Rust Enum documentation

group: rust-hashmap

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