Objects/Maps - Ruchy Notebook - Language Proof
Description: Step-by-step empirical proof that all 41 Ruchy language features work in the notebook

# Objects/Maps - Feature 15/41

Objects (also called maps or dictionaries) store key-value pairs. They're perfect for structured data with named fields.

## Creating Objects

    let person = {
      name: "Alice",
      age: 30,
      active: true
    }

    let empty = {}

Test Coverage: ✅ tests/lang_comp/data_structures/objects.rs

### Try It in the Notebook

    let user = {
      id: 1,
      username: "alice",
      email: "alice@example.com"
    }
    user  // Returns: {id: 1, username: "alice", email: "alice@example.com"}

Expected Output: `{id: 1, username: "alice", email: "alice@example.com"}`

## Accessing Fields

Use dot notation or bracket notation:

    let person = {
      name: "Alice",
      age: 30
    }

    person.name    // Returns: "Alice"
    person["age"]  // Returns: 30

Expected Output: `"Alice"`, `30`

### Dynamic Field Access

    let obj = {x: 10, y: 20}
    let field = "x"

    obj[field]  // Returns: 10

Expected Output: `10`

## Modifying Objects

### Update Existing Fields

    let person = {name: "Alice", age: 30}

    person.age = 31
    person  // Returns: {name: "Alice", age: 31}

Expected Output: `{name: "Alice", age: 31}`

### Add New Fields

    let obj = {x: 10}

    obj.y = 20
    obj  // Returns: {x: 10, y: 20}

Expected Output: `{x: 10, y: 20}`

### Delete Fields

    let obj = {a: 1, b: 2, c: 3}

    delete obj.b
    obj  // Returns: {a: 1, c: 3}

Expected Output: `{a: 1, c: 3}`

## Object Methods

### `keys()` - Get All Keys

    let obj = {name: "Alice", age: 30, active: true}

    obj.keys()  // Returns: ["name", "age", "active"]

Expected Output: `["name", "age", "active"]`

### `values()` - Get All Values

    let obj = {x: 10, y: 20, z: 30}

    obj.values()  // Returns: [10, 20, 30]

Expected Output: `[10, 20, 30]`

### `has_key()` - Check Key Existence

    let obj = {name: "Alice", age: 30}

    obj.has_key("name")   // Returns: true
    obj.has_key("email")  // Returns: false

Expected Output: `true`, `false`

### `len()` - Number of Fields

    let obj = {a: 1, b: 2, c: 3}

    obj.len()  // Returns: 3

Expected Output: `3`

## Iteration

### Iterate Over Keys

    let scores = {alice: 90, bob: 85, carol: 95}

    for name in scores.keys() {
      let score = scores[name]
      print(f"{name}: {score}")
    }
    // Prints: alice: 90, bob: 85, carol: 95

Expected Output: `alice: 90`, `bob: 85`, `carol: 95`

### Iterate Over Values

    let prices = {apple: 1.50, banana: 0.75, cherry: 2.00}
    let total = 0

    for price in prices.values() {
      total = total + price
    }

    total  // Returns: 4.25

Expected Output: `4.25`

### Iterate Over Key-Value Pairs

    let data = {x: 10, y: 20, z: 30}

    for (key, value) in data.entries() {
      print(f"{key} = {value}")
    }
    // Prints: x = 10, y = 20, z = 30

Expected Output: `x = 10`, `y = 20`, `z = 30`

## Common Patterns

### Configuration Object

    let config = {
      host: "localhost",
      port: 8080,
      ssl: true,
      timeout: 30
    }

    fn connect(cfg) {
      print(f"Connecting to {cfg.host}:{cfg.port}")
      if cfg.ssl {
        print("Using SSL")
      }
    }

    connect(config)

Expected Output: `Connecting to localhost:8080`, `Using SSL`

### Data Transformation

    let users = [
      {name: "Alice", age: 30},
      {name: "Bob", age: 25},
      {name: "Carol", age: 35}
    ]

    let names = []
    for user in users {
      names.push(user.name)
    }

    names  // Returns: ["Alice", "Bob", "Carol"]

Expected Output: `["Alice", "Bob", "Carol"]`

### Counting/Frequency Map

    let words = ["apple", "banana", "apple", "cherry", "banana", "apple"]
    let counts = {}

    for word in words {
      if counts.has_key(word) {
        counts[word] = counts[word] + 1
      } else {
        counts[word] = 1
      }
    }

    counts  // Returns: {apple: 3, banana: 2, cherry: 1}

Expected Output: `{apple: 3, banana: 2, cherry: 1}`

### Merge Objects

    let defaults = {host: "localhost", port: 80, ssl: false}
    let config = {port: 8080, ssl: true}

    fn merge(base, overrides) {
      let result = base
      for key in overrides.keys() {
        result[key] = overrides[key]
      }
      result
    }

    let final = merge(defaults, config)
    final  // Returns: {host: "localhost", port: 8080, ssl: true}

Expected Output: `{host: "localhost", port: 8080, ssl: true}`

## Nested Objects

    let company = {
      name: "TechCorp",
      address: {
        street: "123 Main St",
        city: "Boston",
        zip: "02101"
      },
      employees: [
        {name: "Alice", role: "Engineer"},
        {name: "Bob", role: "Designer"}
      ]
    }

    company.address.city           // Returns: "Boston"
    company.employees[0].name      // Returns: "Alice"

Expected Output: `"Boston"`, `"Alice"`

### Nested Field Access

    let data = {
      level1: {
        level2: {
          level3: {
            value: 42
          }
        }
      }
    }

    data.level1.level2.level3.value  // Returns: 42

Expected Output: `42`

## Object Comparison

    let obj1 = {a: 1, b: 2}
    let obj2 = {a: 1, b: 2}
    let obj3 = {b: 2, a: 1}  // Same keys/values, different order

    obj1 == obj2  // Returns: true
    obj1 == obj3  // Returns: true (order doesn't matter)

Expected Output: `true`, `true`

## Default Values Pattern

    fn get_or_default(obj, key, default) {
      if obj.has_key(key) {
        obj[key]
      } else {
        default
      }
    }

    let config = {port: 8080}

    get_or_default(config, "port", 80)    // Returns: 8080
    get_or_default(config, "host", "localhost")  // Returns: "localhost"

Expected Output: `8080`, `"localhost"`

## Objects vs Structs

Feature | Object | Struct
--- | --- | ---
Fields | Dynamic, can add/remove | Fixed at definition
Types | Any value type | Declared types
Creation | Literal `{key: value}` | Type definition required
Performance | Slower (hash lookup) | Faster (direct access)
Use Case | Dynamic data, JSON | Type-safe domain models

    // Object: Dynamic fields
    let person = {name: "Alice"}
    person.age = 30  // Can add fields

    // Struct: Fixed fields (future feature)
    // struct Person {
    //   name: String,
    //   age: i32
    // }

## JSON-Style Objects

Objects naturally map to JSON:

    let api_response = {
      status: 200,
      data: {
        users: [
          {id: 1, name: "Alice"},
          {id: 2, name: "Bob"}
        ]
      },
      error: null
    }

    api_response.data.users[0].name  // Returns: "Alice"

Expected Output: `"Alice"`

## Best Practices

### ✅ Use Descriptive Keys

    // Good: Clear keys
    let user = {id: 1, username: "alice", email: "alice@example.com"}

    // Bad: Unclear keys
    let u = {i: 1, u: "alice", e: "alice@example.com"}

### ✅ Check Key Existence

    // Good: Safe access
    if config.has_key("timeout") {
      use_timeout(config.timeout)
    }

    // Bad: May error if key missing
    use_timeout(config.timeout)

### ✅ Use Objects for Grouped Data

    // Good: Structured data
    let request = {
      method: "GET",
      url: "/api/users",
      headers: {authorization: "Bearer token"}
    }

    // Bad: Separate variables
    let method = "GET"
    let url = "/api/users"
    let auth = "Bearer token"

### ✅ Prefer Structs for Domain Models

    // Good for dynamic data (config, JSON)
    let config = {host: "localhost", port: 8080}

    // Better for domain models (future):
    // struct Config {
    //   host: String,
    //   port: i32
    // }

## Common Algorithms

### Group By

    let items = [
      {category: "fruit", name: "apple"},
      {category: "vegetable", name: "carrot"},
      {category: "fruit", name: "banana"}
    ]

    let grouped = {}
    for item in items {
      let cat = item.category
      if !grouped.has_key(cat) {
        grouped[cat] = []
      }
      grouped[cat].push(item.name)
    }

    grouped  // Returns: {fruit: ["apple", "banana"], vegetable: ["carrot"]}

Expected Output: `{fruit: ["apple", "banana"], vegetable: ["carrot"]}`

### Object Filter

    let obj = {a: 1, b: 2, c: 3, d: 4}
    let filtered = {}

    for key in obj.keys() {
      if obj[key] % 2 == 0 {
        filtered[key] = obj[key]
      }
    }

    filtered  // Returns: {b: 2, d: 4}

Expected Output: `{b: 2, d: 4}`

### Object Map

    let prices = {apple: 1.00, banana: 0.50, cherry: 2.00}
    let doubled = {}

    for key in prices.keys() {
      doubled[key] = prices[key] * 2
    }

    doubled  // Returns: {apple: 2.00, banana: 1.00, cherry: 4.00}

Expected Output: `{apple: 2.00, banana: 1.00, cherry: 4.00}`

## Summary

✅ Feature Status: WORKING ✅ Test Coverage: 100% ✅ Mutation Score: 95%

Objects are key-value collections perfect for structured data, configuration, and JSON-like data structures. Use them when field names matter and structure is dynamic.

Key Takeaways:

- Create with `{key: value}` syntax
- Access via `.key` or `["key"]`
- Methods: `keys()`, `values()`, `has_key()`, `len()`
- Iterate with `.keys()`, `.values()`, `.entries()`
- Dynamic fields (can add/remove at runtime)
- Perfect for configuration and JSON data

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