Structs: Derive and Validation

Eq on Color, Clone on Config, and all three traits together on Vec3.

// Feature: `@derive(Trait, ...)` — generates common implementations
// Syntax: `@derive(Eq)`, `@derive(Clone)`, `@derive(Debug)`, or multiple.
// When to use: structs where you want to compare (`==`), copy (`.clone()`),
// or print (`tostring`) without writing boilerplate.

@derive(Eq)
struct Color {
  r: int,
  g: int,
  b: int,
}

let red = Color { r: 255, g: 0, b: 0 }
let also_red = Color { r: 255, g: 0, b: 0 }
let blue = Color { r: 0, g: 0, b: 255 }

print("red == also_red? {red == also_red}")
// expected: red == also_red? true
print("red == blue? {red == blue}")

// expected: red == blue? false

@derive(Clone)
struct Config {
  host: str,
  port: int,
}

let cfg = Config { host: "localhost", port: 8080 }
let backup = cfg.clone()
print("backup = {backup.host}:{backup.port}")

// expected: backup = localhost:8080

// Multi-derive — several capabilities in a single line.
@derive(Debug, Clone, Eq)
struct Vec3 {
  x: float,
  y: float,
  z: float,
}

let v = Vec3 { x: 1.0, y: 2.0, z: 3.0 }
let w = v.clone()
print(v)
// expected: Vec3 { x: 1.0, y: 2.0, z: 3.0 }
print("v == w? {v == w}")
// expected: v == w? true

Simple struct validation and composition with @serialize.

// Feature: `@validate` — generates `.validate()` that checks for non-nil fields
// Syntax: `@validate` on a struct. The method returns `true` if all
// fields are non-nil.
// When to use: simple payload validation (form, API body) before
// processing.

@validate
struct Registration {
  username: str,
  email: str,
  age: int,
}

let valid = Registration { username: "alice", email: "[email protected]", age: 25 }
print("valid? {valid.validate()}")

// expected: valid? true

// `@validate` also pairs well with @serialize/@deserialize.
@validate
@serialize
struct LoginRequest {
  user: str,
  password: str,
}

let req = LoginRequest { user: "bob", password: "secret" }
print("login valid? {req.validate()}")
// expected: login valid? true
print("login json = {req.to_json()}")
// expected: login json = {"user":"bob","password":"secret"}