Rust: What is the difference between struct and enum?

Struct — custom type with fields (single shape). Enum — type with multiple variants.

Struct:

• All fields exist simultaneously.
• Three forms: named, tuple, unit.
• Methods via impl blocks.
• Represents "this thing has these properties."

1struct Config {
2    host: String,
3    port: u16,
4}
5
6impl Config {
7    fn new(host: &str, port: u16) -> Self {
8        Self { host: host.to_string(), port }
9    }
10}

Enum:

• One of several variants.
• Variants can hold data.
• Pattern matching with match.
• Represents "this thing is one of these."

1enum Event {
2    Click(u32, u32),
3    Key(char),
4    Resize(u32, u32),
5}
6
7fn handle(event: Event) {
8    match event {
9        Event::Click(x, y) => println!("Click at ({}, {})", x, y),
10        Event::Key(c) => println!("Key: {}", c),
11        Event::Resize(w, h) => println!("Resize: {}x{}", w, h),
12    }
13}

When to use:

• Structs for data containers.
• Enums for multiple kinds of values.
• Enums for state machines.

Common mistakes:

• Forgetting a variant in match.
• Using enums when structs are simpler.
• Not deriving common traits.