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:

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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");
    drink("still water");
}
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The first call to drink works. The second panics and thus the third is never called.