Assigning A String Moves Its Ownership

Assignment doesn’t always create an independent copy in Rust. For a heap-backed type such as String, an assignment normally transfers ownership to the new variable in source

fn main() {
    let first = String::from("Server started");
    let second = first;
 
    println!("{second}");
}

After this assignment, second owns the string. Rust copies the pointer, length and capacity into second but it doesn’t copy all the characters into a new heap allocation and then Rust considers first invalid. So, if you’ll run this code, then the compiler will complain:

fn main() {
    let first = String::from("Server started");
    let second = first;
 
    println!("{first}");
    println!("{second}");
}

Transclude of rust-move

A move is usually much cheaper than copying all the underlying data. If the string contained ten megabytes of log data, the move would transfer responsibility for the existing allocation, it would not copy those ten megabytes into another allocation, we call this Rust Move Semantics