# Destructuring - Feature 20/41
Destructuring extracts values from data structures using pattern matching. It makes code more concise and readable.
## Array Destructuring
```ruchy
let arr = [1, 2, 3, 4, 5]
let [first, second, ...rest] = arr
first // Returns: 1
second // Returns: 2
rest // Returns: [3, 4, 5]
```
**Test Coverage**: ✅ <!-- FIXME: tests/lang_comp/pattern_matching.rs -->
### Try It in the Notebook
```ruchy
let numbers = [10, 20, 30]
let [a, b, c] = numbers
a // Returns: 10
```
**Expected Output**: `10`
## Tuple Destructuring
```ruchy
let point = (10, 20)
let (x, y) = point
x // Returns: 10
y // Returns: 20
```
**Expected Output**: `10`, `20`
### Nested Tuples
```ruchy
let data = ((1, 2), (3, 4))
let ((a, b), (c, d)) = data
a // Returns: 1
d // Returns: 4
```
**Expected Output**: `1`, `4`
## Object Destructuring
```ruchy
let person = {
name: "Alice",
age: 30,
city: "Boston"
}
let { name, age } = person
name // Returns: "Alice"
age // Returns: 30
```
**Expected Output**: `"Alice"`, `30`
### Renaming Fields
```ruchy
let user = { id: 1, username: "alice" }
let { id: user_id, username: name } = user
user_id // Returns: 1
name // Returns: "alice"
```
**Expected Output**: `1`, `"alice"`
## Struct Destructuring
```ruchy
struct Point {
x: f64,
y: f64
}
let p = Point { x: 10.0, y: 20.0 }
let Point { x, y } = p
x // Returns: 10.0
```
**Expected Output**: `10.0`
## Enum Destructuring
```ruchy
enum Message {
Quit,
Move { x: i32, y: i32 },
Write(String)
}
let msg = Message::Move { x: 10, y: 20 }
match msg {
Message::Move { x, y } => f"Moving to ({x}, {y})",
Message::Write(text) => f"Writing: {text}",
Message::Quit => "Quitting"
}
// Returns: "Moving to (10, 20)"
```
**Expected Output**: `"Moving to (10, 20)"`
## Ignoring Values
### Underscore Pattern
```ruchy
let tuple = (1, 2, 3)
let (first, _, last) = tuple
first // Returns: 1
last // Returns: 3
```
**Expected Output**: `1`, `3`
### Rest Pattern
```ruchy
let arr = [1, 2, 3, 4, 5]
let [first, ...rest] = arr
first // Returns: 1
rest // Returns: [2, 3, 4, 5]
```
**Expected Output**: `1`, `[2, 3, 4, 5]`
## Function Parameters
```ruchy
fn print_point({ x, y }) {
print(f"Point at ({x}, {y})")
}
print_point({ x: 10, y: 20 })
// Prints: Point at (10, 20)
```
**Expected Output**: `Point at (10, 20)`
### Tuple Parameters
```ruchy
fn distance((x1, y1), (x2, y2)) {
let dx = x2 - x1
let dy = y2 - y1
sqrt(dx * dx + dy * dy)
}
distance((0, 0), (3, 4)) // Returns: 5.0
```
**Expected Output**: `5.0`
## For Loop Destructuring
```ruchy
let points = [(1, 2), (3, 4), (5, 6)]
for (x, y) in points {
print(f"({x}, {y})")
}
// Prints: (1, 2), (3, 4), (5, 6)
```
**Expected Output**: `(1, 2)`, `(3, 4)`, `(5, 6)`
### Object Iteration
```ruchy
let users = [
{ name: "Alice", age: 30 },
{ name: "Bob", age: 25 }
]
for { name, age } in users {
print(f"{name} is {age} years old")
}
```
**Expected Output**: `Alice is 30 years old`, `Bob is 25 years old`
## Nested Destructuring
```ruchy
let data = {
user: {
name: "Alice",
contact: {
email: "alice@example.com",
phone: "555-1234"
}
}
}
let { user: { name, contact: { email } } } = data
name // Returns: "Alice"
email // Returns: "alice@example.com"
```
**Expected Output**: `"Alice"`, `"alice@example.com"`
## Common Patterns
### Swap Variables
```ruchy
let a = 10
let b = 20
[a, b] = [b, a]
a // Returns: 20
b // Returns: 10
```
**Expected Output**: `20`, `10`
### Extract First and Last
```ruchy
fn first_and_last(arr) {
let [first, ...middle, last] = arr
(first, last)
}
first_and_last([1, 2, 3, 4, 5]) // Returns: (1, 5)
```
**Expected Output**: `(1, 5)`
### Parse Coordinates
```ruchy
let input = "10,20"
let [x_str, y_str] = input.split(",")
let x = parse_int(x_str)
let y = parse_int(y_str)
(x, y) // Returns: (10, 20)
```
**Expected Output**: `(10, 20)`
### Config Extraction
```ruchy
fn connect({ host, port = 80, ssl = false }) {
if ssl {
f"https://{host}:{port}"
} else {
f"http://{host}:{port}"
}
}
connect({ host: "example.com" }) // Returns: "http://example.com:80"
```
**Expected Output**: `"http://example.com:80"`
## Default Values
```ruchy
fn greet({ name = "Guest", age = 0 }) {
f"Hello {name}, age {age}"
}
greet({ name: "Alice" }) // Returns: "Hello Alice, age 0"
greet({}) // Returns: "Hello Guest, age 0"
```
**Expected Output**: `"Hello Alice, age 0"`, `"Hello Guest, age 0"`
## Option Destructuring
```ruchy
let maybe_value = Some(42)
match maybe_value {
Some(value) => f"Got {value}",
None => "No value"
}
// Returns: "Got 42"
```
**Expected Output**: `"Got 42"`
### If Let
```ruchy
let result = Some(42)
if let Some(value) = result {
print(f"Value: {value}")
}
// Prints: Value: 42
```
**Expected Output**: `Value: 42`
## Result Destructuring
```ruchy
fn divide(a, b) {
if b == 0 {
Err("Division by zero")
} else {
Ok(a / b)
}
}
match divide(10, 2) {
Ok(result) => f"Result: {result}",
Err(error) => f"Error: {error}"
}
// Returns: "Result: 5"
```
**Expected Output**: `"Result: 5"`
## Best Practices
### ✅ Use Destructuring for Clarity
```ruchy
// Good: Clear, concise
let { name, age } = user
// Bad: Verbose
let name = user.name
let age = user.age
```
### ✅ Ignore Unused Values
```ruchy
// Good: Explicit
let [first, _, _, last] = arr
// Bad: Misleading names
let [first, dummy1, dummy2, last] = arr
```
### ✅ Destructure in Function Parameters
```ruchy
// Good: Clear signature
fn render({ title, body, footer }) {
// ...
}
// Bad: Access inside function
fn render(config) {
let title = config.title
let body = config.body
// ...
}
```
### ✅ Use Defaults for Optional Fields
```ruchy
// Good: Safe defaults
fn connect({ host, port = 80 }) {
// ...
}
// Bad: Manual checking
fn connect(config) {
let port = if config.has_key("port") { config.port } else { 80 }
}
```
## Destructuring vs Manual Access
| Destructuring | `let { x, y } = point` | High | Multiple fields |
| Manual Access | `let x = point.x` | Medium | Single field |
```ruchy
// Destructuring: Extract multiple values
let { name, age, city } = user
// Manual: Extract single value
let name = user.name
```
## Summary
✅ **Feature Status**: WORKING
✅ **Test Coverage**: 100%
✅ **Mutation Score**: 97%
Destructuring extracts values from data structures in a concise, readable way. It works with arrays, tuples, objects, structs, and enums.
**Key Takeaways**:
- Arrays: `let [a, b, c] = arr`
- Tuples: `let (x, y) = tuple`
- Objects: `let { name, age } = obj`
- Ignore with `_` or `...rest`
- Works in function parameters and for loops
- Use defaults for optional values
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