Move Semantics

An assignment will transfer ownership between variables:

fn main() {
    let s1: String = String::from("Hello!");
    let s2: String = s1;
    println!("s2: {s2}");
    // println!("s1: {s1}");
}

The assignment of s1 to s2 transfers ownership.
The data was moved from s1 and s1 is no longer accessible.
When s1 goes out of scope, nothing happens: it has no ownership.
When s2 goes out of scope, the string data is freed.
There is always exactly one variable binding which owns a value.

Mention that this is the opposite of the defaults in C++, which copies by value unless you use std::move (and the move constructor is defined!).
In Rust, you clones are explicit (by using clone).