What happens when a variable goes out of scope

When a variable goes out of scope in Rust, the compiler automatically calls drop to free its memory if it owns data on the heap. If the variable was moved or implements the Copy trait, no special cleanup occurs.

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

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

When a variable leaves its active area, Rust automatically cleans up the memory it was using. This prevents memory leaks by ensuring resources are released immediately when they are no longer needed. Think of it like a library book that is automatically returned to the shelf the moment you leave the library building.