README.md

Exceptions

Example	Topic
BasicHandle	try/catch/throw, custom exceptions, catch order, rethrow, nested exceptions
ThrowNoexcept	noexcept specifier and operator, std::terminate, noexcept moves in std::vector
ErrorCode	std::error_code, std::system_error, errno, and the exception safety guarantees (draft)

1. The mechanism

try {
  mightThrow();
} catch (const MyError& e) {      // most specific first
  ...
} catch (const std::exception& e) {
  ...
} catch (...) {                   // anything else
  throw;                          // rethrow the current exception unchanged
}

When an exception is thrown, the stack unwinds: destructors of all fully constructed local objects run until a matching catch is found. This makes RAII the foundation of exception safety.

2. Guidelines

• Throw by value, catch by const&. This avoids copies and object slicing.
• Derive your exceptions from std::exception, usually std::runtime_error or std::logic_error.
• Use exceptions for exceptional situations. For an expected "no result", std::optional is often clearer (see core/utils/Optional).
• Never let an exception escape a destructor. Destructors are noexcept by default.
• Mark move constructors and move assignment noexcept; containers rely on it (see the ThrowNoexcept example).

3. Exception safety guarantees

Guarantee	Meaning
no-throw	the operation never throws (noexcept)
strong	on failure the state is unchanged ("commit or rollback", e.g. copy-and-swap)
basic	on failure no resources leak and objects stay valid, but may have changed
none	anything can happen - avoid