Wawancara Rust menguji pemahaman terhadap sistem ownership yang unik, manajemen memori tanpa garbage collector, dan kemampuan menulis kode concurrent yang aman. Panduan ini mencakup pertanyaan-pertanyaan esensial, mulai dari dasar-dasar ownership hingga pola async dan concurrency tingkat lanjut. Pewawancara menghargai penjelasan yang menunjukkan pemahaman terhadap jaminan keamanan memori Rust. Menjelaskan bagaimana compiler mencegah bug pada saat kompilasi menjadi pembeda utama. ## Ownership dan Borrowing ### Pertanyaan 1: Jelaskan sistem ownership Rust Ownership adalah konsep sentral Rust yang memungkinkan manajemen memori tanpa garbage collector sekaligus menjamin keamanan memori pada saat kompilasi. ```rust // ownership_basics.rs // The three fundamental rules of ownership fn main() { // Rule 1: Each value has a single owner let s1 = String::from("hello"); // s1 is the owner // Rule 2: Only one variable can own a value at a time let s2 = s1; // s1 is MOVED to s2 // println!("{}", s1); // ERROR: s1 is no longer valid println!("{}", s2); // OK: s2 is now the owner // Rule 3: When the owner goes out of scope, the value is dropped { let s3 = String::from("world"); // s3 is valid here } // s3 goes out of scope, memory is automatically freed // Copy types: simple types are copied, not moved let x = 5; let y = x; // x is COPIED, not moved println!("x = {}, y = {}", x, y); // Both are valid } // Move in action with functions fn take_ownership(s: String) { // s takes ownership of the String println!("{}", s); } // s is dropped here, memory freed fn makes_copy(i: i32) { // i is a copy of the argument println!("{}", i); } // i goes out of scope, nothing special (Copy type) fn ownership_with_functions() { let s = String::from("hello"); take_ownership(s); // s is moved into the function // println!("{}", s); // ERROR: s is no longer valid let x = 5; makes_copy(x); // x is copied println!("{}", x); // OK: x is still valid } ``` Ownership menghilangkan bug memori umum: use-after-free, double-free, dan memory leak. Compiler menjamin properti ini pada saat kompilasi. ### Pertanyaan 2: Apa perbedaan antara immutable dan mutable borrowing? Borrowing memungkinkan penggunaan nilai tanpa mengambil ownership, dengan aturan ketat untuk mencegah data race. ```rust // borrowing_rules.rs // Immutable and mutable references fn main() { let mut s = String::from("hello"); // IMMUTABLE REFERENCES (&T) // Can coexist in unlimited numbers let r1 = &s; // immutable reference let r2 = &s; // another immutable reference println!("{} and {}", r1, r2); // OK // MUTABLE REFERENCE (&mut T) // Only one at a time, and no simultaneous immutable references let r3 = &mut s; // mutable reference // let r4 = &s; // ERROR: cannot have both immutable and mutable // let r5 = &mut s; // ERROR: only one mutable reference allowed r3.push_str(" world"); println!("{}", r3); // Reference scopes are limited to their last use let r6 = &s; // OK because r3 is no longer used println!("{}", r6); } // Practical example: modifying a struct struct User { name: String, age: u32, } impl User { // &self: read-only access fn get_name(&self) -> &str { &self.name } // &mut self: modification access fn set_name(&mut self, name: String) { self.name = name; } // self: takes ownership (consumes the instance) fn into_name(self) -> String { self.name // The User instance no longer exists after this } } fn borrowing_with_structs() { let mut user = User { name: String::from("Alice"), age: 30, }; // Reading println!("Name: {}", user.get_name()); // Modifying user.set_name(String::from("Bob")); // Consuming let name = user.into_name(); // user.age; // ERROR: user has been consumed } ``` Aturan-aturan ini menjamin tidak adanya data race pada saat kompilasi. Tidak ada bahasa lain yang menawarkan jaminan ini tanpa pengorbanan performa. Sejak Rust 2018, compiler menggunakan NLL (Non-Lexical Lifetimes) untuk menentukan secara lebih presisi kapan referensi tidak lagi digunakan, sehingga memberikan fleksibilitas lebih. ### Pertanyaan 3: Apa itu lifetime dan kapan harus dianotasi? Lifetime adalah anotasi yang memberi tahu compiler berapa lama referensi valid, sehingga mencegah dangling reference. ```rust // lifetimes.rs // Understanding and annotating lifetimes // ERROR: dangling reference // fn dangling() -> &String { // let s = String::from("hello"); // &s // s is dropped at function end, reference invalid // } // The compiler often infers lifetimes automatically fn first_word(s: &str) -> &str { // Elided lifetime: compiler understands the return // has the same lifetime as the input match s.find(' ') { Some(i) => &s[..i], None => s, } } // Explicit annotation needed with multiple references fn longest<'a>(x: &'a str, y: &'a str) -> &'a str { // 'a means: the return lives at least as long // as the shorter of the two inputs if x.len() > y.len() { x } else { y } } fn lifetime_example() { let string1 = String::from("long string"); let result; { let string2 = String::from("xyz"); result = longest(&string1, &string2); println!("Longest: {}", result); // OK here } // println!("{}", result); // ERROR: string2 is dropped } // Lifetimes in structs struct ImportantExcerpt<'a> { part: &'a str, // Struct cannot outlive part } impl<'a> ImportantExcerpt<'a> { // Method returning a reference with the same lifetime fn level(&self) -> i32 { 3 } // Elided lifetime for &self returning a new reference fn announce_and_return_part(&self, announcement: &str) -> &str { println!("Attention: {}", announcement); self.part // Returns with lifetime 'a } } // Static lifetime: lives for the entire program duration fn static_lifetime() { let s: &'static str = "hello"; // Stored in the binary // Constants have implicit 'static lifetime const MAX_POINTS: u32 = 100_000; } // Combining lifetimes and generics fn longest_with_announcement<'a, T>( x: &'a str, y: &'a str, ann: T, ) -> &'a str where T: std::fmt::Display, { println!("Announcement: {}", ann); if x.len() > y.len() { x } else { y } } ``` Lifetime diverifikasi pada saat kompilasi. Jika kode berhasil dikompilasi, referensi dijamin valid. ## Trait dan Generics ### Pertanyaan 4: Bagaimana cara kerja trait di Rust? Trait mendefinisikan perilaku bersama antar tipe yang berbeda, mirip dengan interface tetapi dengan fitur tambahan. ```rust // traits_basics.rs // Defining and implementing traits // Trait definition trait Summary { // Required method (no body) fn summarize(&self) -> String; // Method with default implementation fn summarize_author(&self) -> String { String::from("(Anonymous)") } // Default method that calls a required method fn full_summary(&self) -> String { format!("By {} - {}", self.summarize_author(), self.summarize()) } } // Implementation for different types struct NewsArticle { headline: String, location: String, author: String, content: String, } impl Summary for NewsArticle { fn summarize(&self) -> String { format!("{}, by {} ({})", self.headline, self.author, self.location) } fn summarize_author(&self) -> String { format!("@{}", self.author) } } struct Tweet { username: String, content: String, reply: bool, retweet: bool, } impl Summary for Tweet { fn summarize(&self) -> String { format!("{}: {}", self.username, self.content) } } // Trait bounds: constraining generics fn notify(item: &T) { println!("Breaking news! {}", item.summarize()); } // Alternative syntax with where fn notify_verbose(item: &T) where T: Summary, { println!("Breaking news! {}", item.summarize()); } // Multiple trait bounds fn notify_complex(item: &T) { println!("{}", item); } // Return a type that implements a trait fn create_summarizable() -> impl Summary { Tweet { username: String::from("rust_lang"), content: String::from("Rust 2026 is amazing!"), reply: false, retweet: false, } } ``` Trait memungkinkan polimorfisme tanpa pewarisan kelas, lebih mengutamakan komposisi daripada pewarisan. ### Pertanyaan 5: Jelaskan perbedaan antara generisitas statis dan dinamis Rust menawarkan dua pendekatan untuk polimorfisme: monomorphization (statis) dan trait object (dinamis). ```rust // static_vs_dynamic_dispatch.rs // Static vs dynamic dispatch trait Animal { fn speak(&self) -> String; fn name(&self) -> &str; } struct Dog { name: String } struct Cat { name: String } impl Animal for Dog { fn speak(&self) -> String { String::from("Woof!") } fn name(&self) -> &str { &self.name } } impl Animal for Cat { fn speak(&self) -> String { String::from("Meow!") } fn name(&self) -> &str { &self.name } } // STATIC DISPATCH (monomorphization) // Compiler generates a version for each concrete type fn make_speak_static(animal: &T) { // At compile time, becomes make_speak_Dog and make_speak_Cat println!("{} says {}", animal.name(), animal.speak()); } // Advantages: inlining possible, no runtime overhead // Disadvantages: larger binary, type must be known at compile time // DYNAMIC DISPATCH (trait objects) // Uses a vtable to resolve methods at runtime fn make_speak_dynamic(animal: &dyn Animal) { // Resolved via a pointer table (vtable) at runtime println!("{} says {}", animal.name(), animal.speak()); } // Advantages: can store different types, smaller binary // Disadvantages: indirection overhead, no inlining fn main() { let dog = Dog { name: String::from("Rex") }; let cat = Cat { name: String::from("Whiskers") }; // Static: type is known at compile time make_speak_static(&dog); make_speak_static(&cat); // Dynamic: type is resolved at runtime make_speak_dynamic(&dog); make_speak_dynamic(&cat); // Heterogeneous collection (requires dynamic dispatch) let animals: Vec> = vec![ Box::new(Dog { name: String::from("Buddy") }), Box::new(Cat { name: String::from("Luna") }), ]; for animal in animals.iter() { println!("{} says {}", animal.name(), animal.speak()); } } // Object safety: not all traits can become trait objects trait ObjectSafe { fn method(&self); // No Self in return type // No generic parameters } // NOT object safe (cannot be dyn NotObjectSafe) trait NotObjectSafe { fn create() -> Self; // Self in return fn generic(&self, t: T); // Generic } ``` Static dispatch lebih diutamakan untuk performa. Dynamic dispatch berguna untuk koleksi heterogen dan fleksibilitas. ## Penanganan Error ### Pertanyaan 6: Bagaimana menangani error dengan Result dan Option? Rust tidak memiliki exception. Penanganan error dilakukan melalui tipe `Result` dan `Option` dengan pattern matching. ```rust // error_handling.rs // Idiomatic error handling in Rust use std::fs::File; use std::io::{self, Read}; // Option: presence or absence of a value fn find_user(id: u32) -> Option { match id { 1 => Some(String::from("Alice")), 2 => Some(String::from("Bob")), _ => None, // No user found } } // Result: success or error fn divide(a: f64, b: f64) -> Result { if b == 0.0 { Err(String::from("Division by zero")) } else { Ok(a / b) } } fn option_combinators() { let user = find_user(1); // Pattern matching match user { Some(name) => println!("Found: {}", name), None => println!("Not found"), } // unwrap_or: default value let name = find_user(99).unwrap_or(String::from("Unknown")); // map: transform the value if present let upper = find_user(1).map(|n| n.to_uppercase()); // and_then (flatMap): chain Options let first_char = find_user(1).and_then(|n| n.chars().next()); // if let: simplified pattern matching if let Some(name) = find_user(2) { println!("User 2 is {}", name); } } fn result_handling() -> Result<(), Box> { // The ? operator propagates errors automatically let result = divide(10.0, 2.0)?; println!("Result: {}", result); // Equivalent to: // let result = match divide(10.0, 2.0) { // Ok(v) => v, // Err(e) => return Err(e.into()), // }; Ok(()) } // File reading with error propagation fn read_file_contents(path: &str) -> Result { let mut file = File::open(path)?; // Propagates error if failure let mut contents = String::new(); file.read_to_string(&mut contents)?; Ok(contents) } // Custom errors #[derive(Debug)] enum AppError { IoError(io::Error), ParseError(String), NotFound(String), } impl std::fmt::Display for AppError { fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result { match self { AppError::IoError(e) => write!(f, "IO error: {}", e), AppError::ParseError(s) => write!(f, "Parse error: {}", s), AppError::NotFound(s) => write!(f, "Not found: {}", s), } } } impl std::error::Error for AppError {} // Automatic conversion with From impl From for AppError { fn from(error: io::Error) -> Self { AppError::IoError(error) } } fn complex_operation() -> Result { let contents = std::fs::read_to_string("config.txt")?; // Auto-convert if contents.is_empty() { return Err(AppError::NotFound(String::from("Config is empty"))); } Ok(contents) } ``` Operator `?` membuat kode ringkas sekaligus memaksa penanganan error secara eksplisit. Tidak ada kejutan saat runtime. `unwrap()` dan `expect()` akan panic jika nilainya None atau Err. Gunakan hanya untuk prototyping atau kasus di mana kegagalan mustahil terjadi. Di produksi, lebih baik gunakan propagasi dengan `?` atau combinator. ### Pertanyaan 7: Bagaimana membuat custom error dengan thiserror? Crate `thiserror` menyederhanakan pembuatan custom error yang ergonomis. ```rust // custom_errors.rs // Custom errors with thiserror use thiserror::Error; // Error definition with derive macro #[derive(Error, Debug)] pub enum DataStoreError { #[error("connection failed: {0}")] ConnectionFailed(String), #[error("query failed: {query}")] QueryFailed { query: String, source: std::io::Error }, #[error("record not found: id={id}")] NotFound { id: u64 }, #[error("invalid data: {0}")] InvalidData(#[from] serde_json::Error), #[error(transparent)] // Delegates Display to source Other(#[from] anyhow::Error), } // Implementation with rich context pub struct DataStore { connection_string: String, } impl DataStore { pub fn connect(conn_str: &str) -> Result { if conn_str.is_empty() { return Err(DataStoreError::ConnectionFailed( "Empty connection string".into() )); } Ok(Self { connection_string: conn_str.to_string() }) } pub fn get_record(&self, id: u64) -> Result { // Query simulation if id == 0 { return Err(DataStoreError::NotFound { id }); } Ok(Record { id, data: format!("Record {}", id) }) } } pub struct Record { pub id: u64, pub data: String, } // Usage with anyhow for applications use anyhow::{Context, Result}; fn application_code() -> Result<()> { let store = DataStore::connect("postgres://localhost/db") .context("Failed to connect to database")?; let record = store.get_record(42) .context("Failed to fetch user record")?; println!("Got: {}", record.data); Ok(()) } // Pattern: converting errors with context fn read_config() -> Result { let contents = std::fs::read_to_string("config.toml") .context("Failed to read config file")?; let config: Config = toml::from_str(&contents) .context("Failed to parse config file")?; Ok(config) } #[derive(Debug)] struct Config { // ... } ``` `thiserror` ideal untuk library (error bertipe), sedangkan `anyhow` cocok untuk aplikasi (fleksibilitas maksimal). ## Smart Pointer ### Pertanyaan 8: Jelaskan Box, Rc, Arc dan RefCell Smart pointer mengelola memori heap dan memungkinkan pola yang tidak bisa dilakukan oleh ownership biasa. ```rust // smart_pointers.rs // Main smart pointers in Rust use std::rc::Rc; use std::sync::Arc; use std::cell::RefCell; // BOX: heap allocation // Used for: recursive types, large types, trait objects fn box_example() { // Simple heap allocation let b = Box::new(5); println!("b = {}", b); // Recursive type (impossible without Box) #[derive(Debug)] enum List { Cons(i32, Box), Nil, } let list = List::Cons(1, Box::new(List::Cons(2, Box::new(List::Cons(3, Box::new(List::Nil)))))); println!("{:?}", list); } // RC: Reference Counting (single-threaded) // Multiple owners for the same data fn rc_example() { let data = Rc::new(vec![1, 2, 3]); // Clone increments the reference counter let data_clone1 = Rc::clone(&data); // count = 2 let data_clone2 = Rc::clone(&data); // count = 3 println!("Reference count: {}", Rc::strong_count(&data)); // 3 // Each clone can read the data println!("data_clone1: {:?}", data_clone1); // Data is freed when the last Rc is dropped } // ARC: Atomic Reference Counting (thread-safe) // Like Rc but usable across threads fn arc_example() { use std::thread; let data = Arc::new(vec![1, 2, 3, 4, 5]); let mut handles = vec![]; for i in 0..3 { let data_clone = Arc::clone(&data); let handle = thread::spawn(move || { // Each thread has its own Arc println!("Thread {}: {:?}", i, data_clone); }); handles.push(handle); } for handle in handles { handle.join().unwrap(); } } // REFCELL: Interior Mutability // Allows mutation even with an immutable reference fn refcell_example() { let data = RefCell::new(5); // borrow() returns an immutable reference println!("Value: {}", *data.borrow()); // borrow_mut() returns a mutable reference *data.borrow_mut() += 1; println!("After mutation: {}", *data.borrow()); // Borrowing rules are checked at RUNTIME // Panics if rules are violated // let r1 = data.borrow(); // let r2 = data.borrow_mut(); // PANIC: already borrowed } // Common combination: Rc> // Multiple owners with possible mutation fn rc_refcell_example() { #[derive(Debug)] struct Node { value: i32, children: Vec>>, } let node1 = Rc::new(RefCell::new(Node { value: 1, children: vec![], })); let node2 = Rc::new(RefCell::new(Node { value: 2, children: vec![Rc::clone(&node1)], // node1 is child of node2 })); // Modify node1 from anywhere node1.borrow_mut().value = 10; println!("node2 child value: {}", node2.borrow().children[0].borrow().value); // 10 } // For threads: Arc> or Arc> fn arc_mutex_example() { use std::sync::Mutex; use std::thread; let counter = Arc::new(Mutex::new(0)); let mut handles = vec![]; for _ in 0..10 { let counter = Arc::clone(&counter); let handle = thread::spawn(move || { let mut num = counter.lock().unwrap(); *num += 1; }); handles.push(handle); } for handle in handles { handle.join().unwrap(); } println!("Final count: {}", *counter.lock().unwrap()); // 10 } ``` Pilih smart pointer yang tepat sesuai konteks: `Box` untuk heap sederhana, `Rc`/`Arc` untuk berbagi, `RefCell`/`Mutex` untuk interior mutability. ## Concurrency ### Pertanyaan 9: Bagaimana Rust menjamin keamanan thread? Sistem tipe Rust mencegah data race pada saat kompilasi melalui trait `Send` dan `Sync`. ```rust // thread_safety.rs // Concurrent safety guarantees use std::thread; use std::sync::{Arc, Mutex, mpsc}; // SEND: a type can be transferred to another thread // SYNC: a type can be shared between threads via references // Most types are Send and Sync automatically // Exceptions: Rc (not Send/Sync), RefCell (not Sync), raw pointers fn send_example() { let data = vec![1, 2, 3]; // Vec is Send, so it can be moved to another thread let handle = thread::spawn(move || { println!("Data in thread: {:?}", data); }); handle.join().unwrap(); } // The compiler prevents concurrency errors fn compile_time_safety() { // This would NOT compile: // let data = std::rc::Rc::new(5); // thread::spawn(move || { // println!("{}", data); // ERROR: Rc is not Send // }); // Solution: use Arc let data = Arc::new(5); let data_clone = Arc::clone(&data); thread::spawn(move || { println!("{}", data_clone); // OK: Arc is Send }); } // Mutex for thread-safe shared mutation fn mutex_pattern() { let counter = Arc::new(Mutex::new(0)); let mut handles = vec![]; for _ in 0..10 { let counter = Arc::clone(&counter); let handle = thread::spawn(move || { // lock() blocks until exclusive access is obtained let mut num = counter.lock().unwrap(); *num += 1; // MutexGuard is dropped here, releasing the lock }); handles.push(handle); } for handle in handles { handle.join().unwrap(); } println!("Result: {}", *counter.lock().unwrap()); } // RwLock for multiple reads / exclusive write fn rwlock_example() { use std::sync::RwLock; let data = Arc::new(RwLock::new(vec![1, 2, 3])); let mut handles = vec![]; // Multiple simultaneous readers for i in 0..3 { let data = Arc::clone(&data); handles.push(thread::spawn(move || { let read = data.read().unwrap(); println!("Reader {}: {:?}", i, *read); })); } // Only one writer at a time { let data = Arc::clone(&data); handles.push(thread::spawn(move || { let mut write = data.write().unwrap(); write.push(4); println!("Writer added 4"); })); } for handle in handles { handle.join().unwrap(); } } // Channels for inter-thread communication fn channel_example() { let (tx, rx) = mpsc::channel(); // Multi-producer, single-consumer // Clone the sender for multiple producers let tx1 = tx.clone(); thread::spawn(move || { tx1.send("from thread 1").unwrap(); }); thread::spawn(move || { tx.send("from thread 2").unwrap(); }); // Receive messages for received in rx { println!("Got: {}", received); } } ``` "Fearless concurrency": jika kode berhasil dikompilasi, tidak ada data race. Compiler adalah garis pertahanan pertama. Jika thread mengalami panic saat memegang Mutex, Mutex tersebut menjadi "poisoned". Pemanggilan `lock()` berikutnya mengembalikan error yang bisa dipulihkan dengan `into_inner()`. ### Pertanyaan 10: Bagaimana cara kerja async/await di Rust? Async di Rust berbasis pada zero-cost Futures, tanpa runtime bawaan dalam bahasa. ```rust // async_await.rs // Asynchronous programming in Rust use tokio::time::{sleep, Duration}; // async fn returns a Future that must be executed async fn fetch_data(url: &str) -> Result { // await suspends execution without blocking the thread let response = reqwest::get(url).await?; let body = response.text().await?; Ok(body) } // Futures are lazy: nothing executes without await or poll async fn lazy_example() { let future = async { println!("This won't print yet"); }; // Nothing happened future.await; // Now it executes } // Parallel execution of futures async fn parallel_execution() { // join! executes multiple futures in parallel let (result1, result2) = tokio::join!( fetch_data("https://api.example.com/1"), fetch_data("https://api.example.com/2"), ); println!("Results: {:?}, {:?}", result1, result2); } // select! for the first completed future async fn race_example() { tokio::select! { result = fetch_data("https://api1.example.com") => { println!("API 1 responded first: {:?}", result); } result = fetch_data("https://api2.example.com") => { println!("API 2 responded first: {:?}", result); } _ = sleep(Duration::from_secs(5)) => { println!("Timeout!"); } } } // Streams: asynchronous iterators use tokio_stream::StreamExt; async fn stream_example() { let mut stream = tokio_stream::iter(vec![1, 2, 3, 4, 5]); while let Some(value) = stream.next().await { println!("Got: {}", value); } } // Spawn for background tasks async fn spawn_tasks() { let handle = tokio::spawn(async { sleep(Duration::from_secs(1)).await; "Task completed" }); println!("Task spawned, doing other work..."); let result = handle.await.unwrap(); println!("Result: {}", result); } // Entry point with tokio #[tokio::main] async fn main() { // The tokio runtime executes futures parallel_execution().await; } // Alternative: multi-threaded or single-threaded runtime #[tokio::main(flavor = "current_thread")] async fn main_single_thread() { // Everything runs on a single thread } #[tokio::main(flavor = "multi_thread", worker_threads = 4)] async fn main_multi_thread() { // Pool of 4 worker threads } ``` Rust async bersifat "bring your own runtime": tokio, async-std, atau smol. Fleksibilitas ini memungkinkan optimasi sesuai kasus penggunaan. ## Pola Tingkat Lanjut ### Pertanyaan 11: Jelaskan pola Builder di Rust Pola Builder bersifat idiomatis di Rust untuk membangun struktur kompleks dengan banyak field opsional. ```rust // builder_pattern.rs // Idiomatic Builder pattern in Rust #[derive(Debug, Clone)] pub struct Server { host: String, port: u16, max_connections: usize, timeout_seconds: u64, tls_enabled: bool, tls_cert_path: Option, } // Builder with consuming approach (ownership) #[derive(Default)] pub struct ServerBuilder { host: String, port: u16, max_connections: usize, timeout_seconds: u64, tls_enabled: bool, tls_cert_path: Option, } impl ServerBuilder { pub fn new() -> Self { Self { host: String::from("localhost"), port: 8080, max_connections: 100, timeout_seconds: 30, tls_enabled: false, tls_cert_path: None, } } // Each method takes self and returns Self for chaining pub fn host(mut self, host: impl Into) -> Self { self.host = host.into(); self } pub fn port(mut self, port: u16) -> Self { self.port = port; self } pub fn max_connections(mut self, max: usize) -> Self { self.max_connections = max; self } pub fn timeout(mut self, seconds: u64) -> Self { self.timeout_seconds = seconds; self } pub fn enable_tls(mut self, cert_path: impl Into) -> Self { self.tls_enabled = true; self.tls_cert_path = Some(cert_path.into()); self } // build() consumes the builder and creates the final structure pub fn build(self) -> Result { if self.tls_enabled && self.tls_cert_path.is_none() { return Err("TLS enabled but no certificate path provided".into()); } Ok(Server { host: self.host, port: self.port, max_connections: self.max_connections, timeout_seconds: self.timeout_seconds, tls_enabled: self.tls_enabled, tls_cert_path: self.tls_cert_path, }) } } // Fluent usage fn create_server() -> Result { ServerBuilder::new() .host("0.0.0.0") .port(443) .max_connections(1000) .timeout(60) .enable_tls("/etc/ssl/cert.pem") .build() } // Alternative with derive macro (typed-builder crate) // #[derive(TypedBuilder)] // pub struct Config { // #[builder(default = "localhost".to_string())] // host: String, // #[builder(default = 8080)] // port: u16, // } // Pattern with type-level validation (typestate pattern) pub struct Unvalidated; pub struct Validated; pub struct Request { url: String, method: String, headers: Vec<(String, String)>, _state: std::marker::PhantomData, } impl Request { pub fn new(url: &str) -> Self { Self { url: url.to_string(), method: "GET".to_string(), headers: vec![], _state: std::marker::PhantomData, } } pub fn method(mut self, method: &str) -> Self { self.method = method.to_string(); self } // validate() changes the state type pub fn validate(self) -> Result, String> { if self.url.is_empty() { return Err("URL cannot be empty".into()); } Ok(Request { url: self.url, method: self.method, headers: self.headers, _state: std::marker::PhantomData, }) } } impl Request { // send() is only available on validated requests pub async fn send(self) -> Result { // Implementation... todo!() } } struct Response; ``` Pola typestate menjamin pada saat kompilasi bahwa operasi tertentu hanya bisa dipanggil dalam state yang benar. ### Pertanyaan 12: Bagaimana mengimplementasi trait untuk tipe eksternal? "Orphan rule" mencegah implementasi trait eksternal untuk tipe eksternal, tetapi ada solusi yang tersedia. ```rust // newtype_pattern.rs // The Newtype pattern to work around the orphan rule use std::fmt; // ORPHAN RULE: cannot implement Display (std) for Vec (std) // impl fmt::Display for Vec { ... } // ERROR // SOLUTION 1: Newtype wrapper struct Wrapper(Vec); impl fmt::Display for Wrapper { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "[{}]", self.0.join(", ")) } } fn newtype_example() { let w = Wrapper(vec![ String::from("hello"), String::from("world"), ]); println!("{}", w); // [hello, world] } // Transparent access with Deref use std::ops::Deref; impl Deref for Wrapper { type Target = Vec; fn deref(&self) -> &Self::Target { &self.0 } } fn deref_example() { let w = Wrapper(vec![String::from("test")]); println!("Length: {}", w.len()); // Calls Vec::len via Deref } // SOLUTION 2: Extension trait (to add methods) trait VecExt { fn first_or_default(&self) -> Option<&T>; } impl VecExt for Vec { fn first_or_default(&self) -> Option<&T> { self.first() } } fn extension_trait_example() { let v = vec![1, 2, 3]; println!("First: {:?}", v.first_or_default()); } // Newtype with domain semantics #[derive(Debug, Clone, PartialEq, Eq, Hash)] struct Email(String); impl Email { pub fn new(email: &str) -> Result { if email.contains('@') && email.contains('.') { Ok(Self(email.to_string())) } else { Err("Invalid email format") } } pub fn as_str(&self) -> &str { &self.0 } } impl fmt::Display for Email { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "{}", self.0) } } #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)] struct UserId(u64); impl UserId { pub fn new(id: u64) -> Self { Self(id) } } // Newtypes add type safety without runtime overhead fn process_user(id: UserId, email: Email) { println!("Processing user {} with email {}", id.0, email); } fn type_safety_example() { let id = UserId::new(42); let email = Email::new("user@example.com").unwrap(); process_user(id, email); // This would not compile: // process_user(email, id); // Types reversed // process_user(UserId::new(42), "string"); // String instead of Email } ``` Newtype tidak memiliki biaya runtime berkat jaminan representasi memori yang identik. ### Pertanyaan 13: Bagaimana menggunakan procedural macro? Procedural macro memungkinkan pembuatan kode pada saat kompilasi, seperti custom derive. ```rust // procedural_macros.rs // Understanding procedural macros // Proc macros are defined in a separate crate with proc-macro = true // Crate: my_derive (Cargo.toml: proc-macro = true) use proc_macro::TokenStream; use quote::quote; use syn::{parse_macro_input, DeriveInput}; // DERIVE MACRO: #[derive(MyTrait)] #[proc_macro_derive(MyDebug)] pub fn my_debug_derive(input: TokenStream) -> TokenStream { // Parse input as a type definition let input = parse_macro_input!(input as DeriveInput); let name = input.ident; // Generate implementation code let expanded = quote! { impl std::fmt::Debug for #name { fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result { write!(f, stringify!(#name)) } } }; TokenStream::from(expanded) } // ATTRIBUTE MACRO: #[my_attribute] #[proc_macro_attribute] pub fn route(attr: TokenStream, item: TokenStream) -> TokenStream { // attr contains the attribute arguments // item contains the annotated element (function, struct, etc.) let method_path = attr.to_string(); // "GET, /users" let input = parse_macro_input!(item as syn::ItemFn); let fn_name = &input.sig.ident; let expanded = quote! { #input // Additionally generated code fn register_#fn_name() { println!("Registered route: {}", #method_path); } }; TokenStream::from(expanded) } // FUNCTION-LIKE MACRO: my_macro!(...) #[proc_macro] pub fn make_answer(_input: TokenStream) -> TokenStream { "fn answer() -> u32 { 42 }".parse().unwrap() } // --- Usage in client code --- // Derive macro #[derive(MyDebug)] struct Point { x: i32, y: i32, } // Attribute macro #[route("GET", "/users")] fn get_users() -> Vec { vec![] } // Function-like macro make_answer!(); // Generates fn answer() -> u32 { 42 } fn main() { let p = Point { x: 1, y: 2 }; println!("{:?}", p); // Uses our MyDebug println!("Answer: {}", answer()); // 42 } struct User; ``` Procedural macro sangat powerful untuk kode berulang: serialisasi, routing web, validasi, dan sebagainya. ## Keamanan Memori dan Unsafe ### Pertanyaan 14: Kapan dan bagaimana menggunakan unsafe? Blok `unsafe` memungkinkan melewati pemeriksaan compiler tertentu untuk kode low-level. ```rust // unsafe_rust.rs // Understanding unsafe and its guarantees // The 5 superpowers of unsafe: // 1. Dereference raw pointers // 2. Call unsafe functions // 3. Access/modify mutable static variables // 4. Implement unsafe traits // 5. Access union fields // RAW POINTERS fn raw_pointers() { let mut num = 5; // Creating raw pointers is safe let r1 = &num as *const i32; let r2 = &mut num as *mut i32; // Dereferencing requires unsafe unsafe { println!("r1 is: {}", *r1); *r2 = 10; println!("r2 is: {}", *r2); } } // UNSAFE FUNCTION // The function guarantees safety IF preconditions are met unsafe fn dangerous() { // Code that assumes the caller verified invariants } fn call_dangerous() { // Must be in an unsafe block unsafe { dangerous(); } } // SAFE ABSTRACTION over unsafe code fn split_at_mut(values: &mut [i32], mid: usize) -> (&mut [i32], &mut [i32]) { let len = values.len(); let ptr = values.as_mut_ptr(); assert!(mid <= len); // Runtime check unsafe { // We know the two slices don't overlap ( std::slice::from_raw_parts_mut(ptr, mid), std::slice::from_raw_parts_mut(ptr.add(mid), len - mid), ) } } // FFI: calling C code extern "C" { fn abs(input: i32) -> i32; } fn call_c_function() { unsafe { println!("Absolute value: {}", abs(-3)); } } // Export a function for C #[no_mangle] pub extern "C" fn call_from_c() { println!("Called from C!"); } // MUTABLE STATIC static mut COUNTER: u32 = 0; fn increment_counter() { unsafe { COUNTER += 1; println!("COUNTER: {}", COUNTER); } } // UNSAFE TRAIT unsafe trait Dangerous { // Implementers guarantee invariants } unsafe impl Dangerous for i32 { // Implementer asserts respecting the trait's invariants } // Practical example: structure with internal pointer pub struct MyVec { ptr: *mut T, len: usize, capacity: usize, } impl MyVec { pub fn new() -> Self { Self { ptr: std::ptr::null_mut(), len: 0, capacity: 0, } } pub fn push(&mut self, value: T) { if self.len == self.capacity { self.grow(); } unsafe { std::ptr::write(self.ptr.add(self.len), value); } self.len += 1; } fn grow(&mut self) { // Unsafe allocation/reallocation... } } impl Drop for MyVec { fn drop(&mut self) { unsafe { // Properly free memory for i in 0..self.len { std::ptr::drop_in_place(self.ptr.add(i)); } if self.capacity > 0 { let layout = std::alloc::Layout::array::(self.capacity).unwrap(); std::alloc::dealloc(self.ptr as *mut u8, layout); } } } } ``` Minimalkan area kode unsafe. Bungkus kode unsafe dalam abstraksi aman yang menjamin invarian. Kode unsafe tidak boleh merusak memori safe di sekitarnya. ### Pertanyaan 15: Bagaimana cara kerja borrow checker? Borrow checker adalah inti dari compiler Rust yang memverifikasi aturan ownership dan borrowing. ```rust // borrow_checker.rs // Understanding how the borrow checker works fn borrow_checker_basics() { let mut v = vec![1, 2, 3]; // RULE 1: Either multiple immutable references or one mutable let r1 = &v; let r2 = &v; println!("{:?} {:?}", r1, r2); // OK: multiple immutable references // From here, r1 and r2 are no longer used (NLL) let r3 = &mut v; // OK thanks to Non-Lexical Lifetimes r3.push(4); } // The borrow checker tracks lifetimes fn lifetime_tracking() { let mut data = String::from("hello"); let slice = &data[..]; // Immutable borrow starts // data.push_str(" world"); // ERROR: cannot mutate during borrow println!("{}", slice); // Last use of slice data.push_str(" world"); // OK: borrow ended } // Common problems and solutions mod common_patterns { // Problem: borrowing two mutable fields struct Data { field1: Vec, field2: Vec, } fn problem(data: &mut Data) { // This sometimes doesn't compile directly: // let f1 = &mut data.field1; // let f2 = &mut data.field2; // Solution: destructuring let Data { field1, field2 } = data; field1.push(1); field2.push(2); } // Problem: iterate and modify fn iterate_and_modify() { let mut v = vec![1, 2, 3, 4, 5]; // Does not compile: // for &x in &v { // if x % 2 == 0 { // v.push(x * 2); // ERROR: borrowed by iterator // } // } // Solution 1: collect indices first let to_add: Vec = v.iter() .filter(|&&x| x % 2 == 0) .map(|&x| x * 2) .collect(); v.extend(to_add); // Solution 2: use explicit indices let len = v.len(); for i in 0..len { if v[i] % 2 == 0 { let new_val = v[i] * 2; v.push(new_val); } } } // Problem: self-referential struct // struct SelfRef { // data: String, // slice: &str, // Reference to data - IMPOSSIBLE // } // Solution: use indices or crates like ouroboros struct SafeSelfRef { data: String, slice_start: usize, slice_end: usize, } impl SafeSelfRef { fn get_slice(&self) -> &str { &self.data[self.slice_start..self.slice_end] } } } // Patterns to work around limitations mod workarounds { use std::cell::RefCell; // Interior mutability when borrow checker is too restrictive struct Graph { nodes: RefCell>, } struct Node { value: i32, } impl Graph { fn add_node(&self, value: i32) { // Mutation possible despite &self self.nodes.borrow_mut().push(Node { value }); } fn get_node(&self, index: usize) -> Option { self.nodes.borrow().get(index).map(|n| n.value) } } } ``` Borrow checker mungkin terasa membatasi pada awalnya, tetapi batasan ini menghilangkan seluruh kategori bug yang ada di bahasa lain. ## Kesimpulan Wawancara Rust mengevaluasi pemahaman mendalam terhadap sistem ownership, jaminan keamanan memori, dan kemampuan menulis kode concurrent tanpa data race. Penguasaan konsep-konsep ini membedakan developer yang mampu memanfaatkan keunggulan unik Rust. ### Daftar Persiapan - Memahami ownership, borrowing, dan tiga aturan fundamental - Mengetahui kapan dan bagaimana menganotasi lifetime - Menguasai trait serta perbedaan antara static dan dynamic dispatch - Menangani error secara idiomatis dengan Result dan Option - Memilih smart pointer yang tepat sesuai konteks - Menulis kode concurrent dengan Arc, Mutex, dan channel - Memahami async/await dan runtime seperti tokio - Mengetahui kapan dan bagaimana menggunakan unsafe secara aman Persiapan wawancara Rust membutuhkan latihan dengan konsep ownership yang unik. Latihan di Exercism, proyek pribadi, dan kontribusi pada ekosistem Rust akan mengkonsolidasikan pengetahuan ini untuk wawancara teknis yang paling menantang.