Panics

In case of a fatal runtime error, Rust triggers a "panic":

# // Copyright 2022 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
fn main() {
    let v = vec![10, 20, 30];
    dbg!(v[100]);
}

• Panics are for unrecoverable and unexpected errors.
  • Panics are symptoms of bugs in the program.
  • Runtime failures like failed bounds checks can panic.
  • Assertions (such as assert!) panic on failure.
  • Purpose-specific panics can use the panic! macro.
• A panic will "unwind" the stack, dropping values just as if the functions had returned.
• Use non-panicking APIs (such as Vec::get) if crashing is not acceptable.

By default, a panic will cause the stack to unwind. The unwinding can be caught:

# // Copyright 2022 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
use std::panic;

fn main() {
    let result = panic::catch_unwind(|| "No problem here!");
    dbg!(result);

    let result = panic::catch_unwind(|| {
        panic!("oh no!");
    });
    dbg!(result);
}

• Catching is unusual; do not attempt to implement exceptions with catch_unwind!
• This can be useful in servers which should keep running even if a single request crashes.
• This does not work if panic = 'abort' is set in your Cargo.toml.