Borrowing Lets A Function Use A Value Without Owning It

Ok, so moving a string into a function makes sense when the function should own it but many functions only need to look at a value temporarily and passing ownership into every one of those functions would become annoying very quickly

To get rid of this annoying situation, we will use the concept of reference

A reference gives access to a value without transferring ownership and creating a reference is called borrowing in source

fn calculate_length(message: &String) -> usize {
    message.len()
}
 
fn main() {
    let message = String::from("Server started");
 
    let length = calculate_length(&message);
 
    println!("{message}");
    println!("Length: {length}");
}

In the calculate_length function, the expression &message creates a reference. The function can use the string throughout that reference but it does not own the string

Transclude of function-borrowing

When calculate_length finishes, the reference goes away and the original String remains because ownership never went away from the main function

When a function only needs read text, accepting &str is usually more flexible than accepting &String

fn inspect(message: &str) {
    println!("{message}");
}