Error Handling

Rust’s commitment to reliability extends to error handling. Errors are a fact of life in software, so Rust has a number of features for handling situations in which something goes wrong. In many cases, Rust will require you to acknowledge the possibility of an error occurring and take some action before your code will compile. This makes your program more robust by ensuring that you won’t only discover errors after you’ve deployed your code to production.

Rust groups errors into two major categories: recoverable and unrecoverable errors. Recoverable errors are situations when it’s usually reasonable to report the problem to the user and retry the operation, like a file not being found. Unrecoverable errors are always symptoms of bugs, like trying to access a location beyond the end of an array.

Most languages don’t distinguish between the two kinds of errors, and handle both in the same way using mechanisms like exceptions. Rust doesn’t have exceptions. Instead, it has the value Result<T, E> for recoverable errors and the panic! macro that stops execution when it encounters unrecoverable errors. This chapter will cover calling panic! first, then talk about returning Result<T, E> values. Finally, we’ll discuss considerations to take into account when deciding whether to try to recover from an error or to stop execution.