Strings

Rust has two main string types. A String is an owned, growable string stored on the heap. A &str (string slice) is a borrowed view into string data, often a literal.

String vs &str

fn main() {
    let literal: &str = "I am a string slice";
    let owned: String = String::from("I am an owned String");
    println!("{}", literal);
    println!("{}", owned);
}

String literals in your code are always &str. Use String when you need to build or modify text at runtime.

Concatenation

fn main() {
    let mut greeting = String::from("Hello");
    greeting.push_str(", world"); // append a &str
    greeting.push('!');           // append a single char
    println!("{}", greeting);

    let a = String::from("foo");
    let b = String::from("bar");
    let combined = a + &b; // a is moved, b is borrowed
    println!("{}", combined);
}

Common methods

fn main() {
    let text = String::from("Rust");
    println!("{}", text.len());          // 4 (bytes)
    println!("{}", text.is_empty());     // false
    println!("{}", text.to_uppercase()); // RUST
    println!("{}", text.contains("us")); // true
}

The format! macro builds a String without moving its inputs, which is often cleaner than chaining +.