error-conversion-guide

Error conversion uses From/Into traits to automatically transform error types. Implement From for your error enum to enable the ? operator to work seamlessly across functions returning different error sources, eliminating manual conversion code.

Define a shared error type and implement From for each error source you need to convert. This lets functions return Result<T, UnifiedError> where the ? operator automatically converts IO, parsing, or custom errors into your unified type.

The #[from] attribute on thiserror enum variants automatically generates From implementations. Each variant can wrap a source error type, so the ? operator converts and propagates errors without writing manual From code.

Yes, map_err transforms one error type into another by applying a conversion function. Use it to adapt Results from external libraries into your unified error type when From implementations aren't suitable.

The ? operator requires the error type to implement From for the source error. If types don't match, the compiler can't auto-convert. Implement From<SourceError> for your error type, or use map_err to manually convert.

From is the primary trait; Into is automatically derived from it. Implement From for your error type to receive source errors, and Into is available for free as the inverse conversion, enabling flexible error handling patterns.