Learn about fatal errors with panic!
Panicking is the simplest error handling mechanism in Rust.
You can use the panic! macro to panic the current thread. The macro prints an error message, frees resources, and then exits the program.
This example shows how to call the panic! macro:
fn main() {
panic!("Farewell!");
}
This program would exit with status code 101 and print the following message:
thread 'main' panicked at 'Farewell!', src/main.rs:2:5
The last part of the preceding panic message shows the location of the panic. It occurred in the src/main.rs file, on the fifth character of the second line.
In general terms, you should use panic! when a program reaches an unrecoverable state. A state where there's absolutely no way to recover from the error.
Rust panics on some operations such as a division by zero or an attempt to access an index that isn't present in an array, a vector, or a hash map, as shown in the following code:
let v = vec![0, 1, 2, 3];
println!("{}", v[6]); // this will cause a panic!
In the next unit, you learn how to handle such errors without causing your program to panic.