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 requires you to acknowledge the possibility of an error occurring and take some action before your code will compile. This requirement makes your program more robust by ensuring that you’ll discover errors and handle them appropriately before you’ve deployed your code to production!

Rust groups errors into two major categories: recoverable and unrecoverable errors. Recoverable errors are situations in which it’s reasonable to report the problem to the user and retry the operation, like a file not found error. 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 these two kinds of errors and handle both in the same way using mechanisms like exceptions. Rust doesn’t have exceptions. Instead, it has the type Result<T, E> for recoverable errors and the panic! macro that stops execution when it encounters unrecoverable errors. This chapter covers calling panic! first and then talks about returning Result<T, E> values. Additionally, we’ll explore considerations to take into account when deciding whether to try to recover from an error or to stop execution.