Status

Accepted

Context

The Enigma Machine Core is designed to be universal, and it targets platforms that do not support exceptions (-fno-exceptions) or where exceptions are discouraged for performance reasons (e.g., Embedded systems, WASM).

Currently, the engine uses:

1. Exceptions: std::runtime_error and std::invalid_argument are thrown in constructors and configuration loaders.
2. Boolean Returns/Logging: Some internal logic reports errors via std::cerr or simple boolean returns.

Decision

We will transition from C++ exceptions to the **std::expected** (C++23) pattern for reporting errors in public and internal APIs.

1. Value-Error Return: Public-facing methods like keyTransform and configuration loaders will return a Result<T> (aliased to std::expected<T, ErrorCode>).
2. No-Exceptions Compatibility: This approach allows us to compile the engine with -fno-exceptions without losing error-reporting capability.
3. Exception-Free Core: After the transition, all throw statements in the core logic will be removed or conditionally enabled for rich targets only.
4. Error Codes: We will define a comprehensive set of ErrorCode values representing configuration failures, validation errors, and runtime issues.

Consequences

• Portability: The engine becomes fully compatible with constrained targets (embedded, WASM).
• API Changes: Most public methods will have their return signatures updated.
• Verbosity: Error checking becomes explicit in the caller, similar to Rust's Result or Go's error handling.
• Dependency: Since we use C++20, we may need a backport (like tl::expected) if C++23 is not yet available in all target compilers.