m06-error-handling

name	m06-error-handling
description	Mastering C++ Error Handling. Triggers: exceptions, try-catch, noexcept, std::expected, std::optional, error codes, assert, terminate. Use when this capability is needed.

C++ 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.

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