Rust Error Handling

Rust groups errors into two major categories: recoverable and unrecoverable.

Unrecoverable Errors with `panic!`

When a program encounters an unrecoverable state (e.g., array out of bounds), it calls the panic! macro.

Behavior: Prints an error message, unwinds/cleans up the stack, and quits.
RUST_BACKTRACE=1: An environment variable that provides a full call stack on panic for easier debugging.

For errors that the program can potentially handle, Rust uses the Result enum:

enum Result<T, E> {
    Ok(T),
    Err(E),
}

Handling: Use match or helper methods like unwrap() (panics on error) and expect("msg") (panics with a custom message).
Propagating Errors: Use the ? operator to return an error from a function to the caller immediately if it occurs.

The ? operator is a concise way to handle Result (and Option).

If the value is Ok(v), it returns v to the current scope.
If the value is Err(e), it returns Err(e) from the entire function.
Requirement: The function's return type must be compatible with the error being propagated (e.g., Result or Option).

Use panic! for examples, prototypes, tests, or when an invariant is broken (bug in the code).
Use Result when failure is an expected possibility (e.g., file not found, network error).