abort and unwind

The previous section illustrates the error handling mechanism panic. Different code paths can be conditionally compiled based on the panic setting. The current values available are unwind and abort.

Building on the prior lemonade example, we explicitly use the panic strategy to exercise different lines of code.

fn drink(beverage: &str) {
    // You shouldn't drink too much sugary beverages.
    if beverage == "lemonade" {
        if cfg!(panic = "abort") {
            println!("This is not your party. Run!!!!");
        } else {
            println!("Spit it out!!!!");
        }
    } else {
        println!("Some refreshing {} is all I need.", beverage);
    }
}

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

Here is another example focusing on rewriting drink() and explicitly use the unwind keyword.

#[cfg(panic = "unwind")]
fn ah() {
    println!("Spit it out!!!!");
}

#[cfg(not(panic = "unwind"))]
fn ah() {
    println!("This is not your party. Run!!!!");
}

fn drink(beverage: &str) {
    if beverage == "lemonade" {
        ah();
    } else {
        println!("Some refreshing {} is all I need.", beverage);
    }
}

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

The panic strategy can be set from the command line by using abort or unwind.

rustc  lemonade.rs -C panic=abort