fn read_username_from_file() -> Result<String, io::Error> let mut s = String::new(); File::open("hello.txt")?.read_to_string(&mut s)?; Ok(s)
let x = 5; let x = x + 1; // shadows previous x { let x = x * 2; println!("Inner: {}", x); // 12 } println!("Outer: {}", x); // 6 Shadowing lets you change type without renaming: ultimate rust crash course
let mut s = String::from("hello"); let r1 = &s; // immutable borrow let r2 = &s; // another immutable borrow // let r3 = &mut s; // ERROR: cannot borrow as mutable Slices let you reference part of a collection without copying. No GC, no runtime overhead
Ownership & Borrowing. The compiler checks memory rules at compile time. No GC, no runtime overhead. If it compiles, it’s memory-safe. Mental model: Think of Rust as C++ with a very strict, helpful compiler that refuses to let you shoot yourself in the foot. 2. Installation & "Hello, World!" Install via rustup.rs . Then: 2. Installation & "Hello
fn main() { let user1 = User active: true, username: String::from("rustacean"), sign_in_count: 1, ; println!("{}", user1.username); } struct Color(i32, i32, i32); let black = Color(0,0,0); Methods (impl block) impl User { fn display(&self) { println!("{} active: {}", self.username, self.active); } } user1.display(); 12. Enums & Pattern Matching Enums are Rust’s way of saying “one of these variants.”
let f = File::open("hello.txt").unwrap(); let f = File::open("hello.txt").expect("Failed to open hello.txt"); Propagate errors with ? operator (inside function returning Result ):