Rust: What is the difference between struct and enum?

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

Struct:

• Defines a type with fields that all exist simultaneously.
• Three forms: named fields, tuple structs, unit structs.
• Supports methods via impl blocks.
• Represents "this thing has these properties."

1// Named fields
2struct User {
3    name: String,
4    email: String,
5    active: bool,
6}
7
8// Tuple struct
9struct Point(f64, f64);
10
11// Unit struct
12struct Marker;

Enum:

• Defines a type that can be one of several variants.
• Variants can hold different data.
• Powerful with match for exhaustive pattern matching.
• Represents "this thing is one of these."

1enum TrafficLight {
2    Red,
3    Yellow,
4    Green,
5}
6
7enum Message {
8    Quit,
9    Move { x: i32, y: i32 },
10    Write(String),
11    ChangeColor(i32, i32, i32),
12}

When to use:

• Structs for data containers with fixed fields.
• Enums when a value can be one of several kinds.
• Enums for state machines, commands, and algebraic data types.

Common mistakes:

• Forgetting a variant in match — compiler enforces exhaustiveness.
• Using enums when all variants have the same fields — use structs.
• Not leveraging #[derive()] for auto-implementation of traits.