The Result Type

The standard approach to recoverable errors uses return-type encoding with a Result type. A function that can fail returns Result<T, E>, where T is the success value and E is the error.

func ReadFile(path: String) -> Result<String, IoError> {
    // Implementation
}

match ReadFile("config.toml") {
    Result::Ok(contents) => ParseConfig(contents),
    Result::Err(err) => Print("Failed: {}", err),
}

Because the error is part of the return type, the caller cannot ignore it by accident — every outcome must be handled, typically by match on the Ok and Err variants.

See Also

• match — destructuring Ok and Err
• Fatal Errors — for conditions a caller is not expected to recover from
• Enumerations — variants with data, the basis of Result