panic

The simplest error handling mechanism we will see is panic. It prints an error message, starts unwinding the stack, and usually exits the program. Here, we explicitly call panic on our error condition:

fn drink(beverage: &str) {
    // You shouldn't drink too much sugary beverages.
    if beverage == "lemonade" { panic!("AAAaaaaa!!!!"); }

    println!("Some refreshing {} is all I need.", beverage);
}

fn main() {
    drink("water");
    drink("lemonade");
}