More on references

References are very important in Rust. Rust uses references to make sure that all memory access is safe. We know that we use & to create a reference:

fn main() {
    let country = String::from("Austria");
    let ref_one = &country;
    let ref_two = &country;

    println!("{}", ref_one);
}

This prints Austria.

In the code, country is a String. We then created two references to country. They have the type &String, which you say is a "reference to a String". We could create three references or one hundred references to country and it would be no problem.

But this is a problem:

fn return_str() -> &str {
    let country = String::from("Austria");
    let country_ref = &country;
    country_ref // ⚠️
}

fn main() {
    let country = return_str();
}

The function return_str() creates a String, then it creates a reference to the String. Then it tries to return the reference. But the String country only lives inside the function, and then it dies. Once a variable is gone, the computer will clean up the memory and use it for something else. So after the function is over, country_ref is referring to memory that is already gone, and that's not okay. Rust prevents us from making a mistake with memory here.

This is the important part about the "owned" type that we talked about above. Because you own a String, you can pass it around. But a &String will die if its String dies, so you don't pass around "ownership" with it.

Easy Rust

More on references