m06-error-handling

Core Question

Is this error recoverable?

• Yes (Local): std::expected or return code.
• Yes (Distant): Exceptions (throw).
• No (Bug): assert or std::terminate.

Error → Design Question

| Issue | Design Question | | ---------------------- | ---------------------------------------------------- | | Uncaught Exception | Did you forget to catch, or throw in noexcept? | | Silent Failure | Did you ignore a return code? (Use [[nodiscard]]). | | Destructor Throw | Never throw from destructor (std::terminate). |

Thinking Prompt

1. Is absence valid?

   • Yes? → std::optional<T>.

2. Does caller need details?

   • Yes? → std::expected<T, E> or Exception.
   • No? → bool or std::optional.

3. Is it a Logic Error (Bug)?

   • Yes? → assert() or std::terminate(). Do not throw for bugs in C++ (Contract Violation).

Trace Up / Down

• Trace Up:
  • Issue: "Program aborted with 'terminate called recursively'."
  • Cause: An exception was thrown while stack unwinding (in a destructor).
  • Fix: Fix the destructor. Ensure RAII cleanup is noexcept.

Quick Reference

| Mechanism | Cost (Happy) | Cost (Sad) | Use When | | ------------------- | -------------- | ---------- | ---------------------------- | | std::optional | Branch | Branch | Return may be empty. | | std::expected | Branch | Branch | Recoverable error (Parsing). | | Exception | Zero | Huge | Rare IO/Resource errors. | | Assert | Zero (Release) | Abort | Logic bugs / Invariants. |