What Happens When a Variable Goes Out of Scope in Rust?

When a variable goes out of scope in Rust, the compiler automatically calls drop to free the memory if the variable owns heap data like a String, but does nothing if the data was moved or is a stack-allocated type like i32. This cleanup happens immediately when the closing brace } is reached, preventing memory leaks without manual intervention.

fn main() {
    let s = String::from("hello"); // s comes into scope
    // s goes out of scope here and is dropped
}

fn takes_ownership(some_string: String) {
    println!("{some_string}");
} // some_string goes out of scope and `drop` is called

Think of scope as a room where a variable lives; when you leave the room, the variable is automatically cleaned up. If the variable held something heavy like a box (heap data), Rust throws it away to save space. If it was just a small number or had already been given to someone else, nothing happens because there is nothing left to clean.