// Immutable User in Rust (Using Default Immutability and No Mutable Bindings)
//
// Rust enforces immutability by default:
//
// 1. Variables are immutable unless declared with `mut`
// 2. Struct fields cannot be changed unless the entire struct is mutable
// 3. No setters = no mutation
// 4. Ownership rules prevent accidental modification
//
// This makes Rust one of the strongest languages for immutability.
//
// Define an immutable User struct
struct User {
id: u32,
name: String,
}
impl User {
// Constructor
fn new(id: u32, name: &str) -> User {
User {
id,
name: name.to_string(),
}
}
// Getter methods (read-only)
fn id(&self) -> u32 {
self.id
}
fn name(&self) -> &str {
&self.name
}
}
fn main() {
// Immutable user (no `mut`)
let user = User::new(42, "Sophia");
println!("ID: {}", user.id());
println!("Name: {}", user.name());
// These lines will NOT compile if uncommented:
//
// user.id = 100; // cannot assign to field of immutable binding
// user.name = "Tom".into(); // cannot assign to field of immutable binding
//
// Rust prevents mutation at compile time, before the program even runs.
// Demonstrate that reading is allowed
let id_copy = user.id();
let name_copy = user.name();
println!("ID copy: {}", id_copy);
println!("Name copy: {}", name_copy);
}
/*
run:
ID: 42
Name: Sophia
ID copy: 42
Name copy: Sophia
*/
