What is the difference between enum and struct?

Question

Accepted Answer

**Enum** — sum type, variants. **Struct** — product type, fields.

**Enum:**
- One variant at a time.
- Pattern matching.
- Algebraic type.

**Struct:**
- All fields present.
- Named fields.
- Record type.

```rust
// Enum
enum Shape {
    Circle(f64),
    Rectangle(f64, f64),
}

// Struct
struct Circle {
    radius: f64,
}
```

**Pattern matching with enum:**
```rust
match shape {
    Shape::Circle(r) => println!("Circle: {}", r),
    Shape::Rectangle(w, h) => println!("Rect: {}x{}", w, h),
}
```

**Key:** Enum for variants, Struct for records.

Rust: What is the difference between enum and struct?