src/doc/book/nostarch/chapter18-destructuring-nested-structs-and-enums.md

#### Destructuring Nested Structs and Enums

Until now, all our examples have been matching structs or enums that were one
level deep. Matching can work on nested items too!

For example, we can refactor the code in Listing 18-15 to support RGB and HSV
colors in the `ChangeColor` message, as shown in Listing 18-16.

```rust
enum Color {
   Rgb(i32, i32, i32),
   Hsv(i32, i32, i32)
}

enum Message {
    Quit,
    Move { x: i32, y: i32 },
    Write(String),
    ChangeColor(Color),
}

fn main() {
    let msg = Message::ChangeColor(Color::Hsv(0, 160, 255));

    match msg {
        Message::ChangeColor(Color::Rgb(r, g, b)) => {
            println!(
                "Change the color to red {}, green {}, and blue {}",
                r,
                g,
                b
            )
        },
        Message::ChangeColor(Color::Hsv(h, s, v)) => {
            println!(
                "Change the color to hue {}, saturation {}, and value {}",
                h,
                s,
                v
            )
        }
        _ => ()
    }
}
```

<span class="caption">Listing 18-16: Matching on nested enums</span>

The pattern of the first arm in the `match` expression matches a
`Message::ChangeColor` enum variant that contains a `Color::Rgb` variant; then
the pattern binds to the three inner `i32` values. The pattern of the second
arm also matches a `Message::ChangeColor` enum variant, but the inner enum
matches the `Color::Hsv` variant instead. We can specify these complex
conditions in one `match` expression, even though two enums are involved.