Option And Result Methods

Option and Result are standard enum values. They are used by the standard library for ordinary absence and recoverable failures; they do not replace VM diagnostics for type errors, denied capabilities, or exhausted budgets.

Constructors And Predicates

Use module constructors when a script needs to create values explicitly.

fn main() {
    let present = option::some(4);
    let missing = option::none();
    let ok = result::ok("ready");
    return present.is_some() && missing.is_none() && ok.is_ok();
}

Both module functions and value methods expose common predicates: is_some, is_none, is_ok, and is_err.

Fallbacks And Conversion

unwrap_or works on both Option and Result. ok_or converts an Option to a Result; to_option and to_error_option inspect a Result.

fn main() {
    let parsed = "42".parse_i64();
    let checked = parsed.ok_or("not a number");
    let value = checked.unwrap_or(0);
    let error = checked.to_error_option().unwrap_or("");
    return value + error.len();
}

flatten removes one layer from nested Option or nested Result values.

Callback Helpers And Propagation

map, and_then, or_else, and filter operate on the success/present path. Result.map_err transforms the error payload.

fn main() {
    let score = "5"
        .parse_i64()
        .map(|value| value * 2)
        .filter(|value| value >= 10)
        .unwrap_or(0);
    return score;
}

The ? operator propagates Option::None or Result::Err from the current function. Use it for script-visible control flow, not for host permission or VM runtime failures.