std::inout_...inout_ptr_t(3)

🌸 NAME 🌸

std::inout_ptr_t::~inout_ptr_t — literally the destructor for std::inout_ptr_t. That’s the whole name, bestie. 💅

✨ Synopsis ✨

Okay so this is from the C++ Standard Libary manual, page std::inout_...inout_ptr_t(3), and the signature is exactly this:

~inout_ptr_t();  (since C++23)

It resets the adapted Smart object by the value of the modified Pointer object (or the void* object if operator void**() has been called) and the captured arguments. release() may be called on the adapted Smart object if it is not called by the constructor. 🫶

Let’s define the cast so nobody gets lost:

• s denotes the adapted Smart object,
• args... denotes the captured arguments,
• p denotes the value of stored Pointer, or static_cast<Pointer>(*operator void**()) if operator void** has been called,
• SP be
  • Smart::pointer, if it is valid and denotes a type, otherwise,
  • Smart::element_type*, if Smart::element_type is valid and denotes a type, otherwise,
  • std::pointer_traits<Smart>::element_type*, if std::pointer_traits<Smart>::element_type is valid and denotes a type, otherwise,
  • Pointer,
• /*do-release*/ denotes s.release() if the constructor does not call release(), empty otherwise.

Now the destructor behavior, in order:

• If Smart is a pointer type, the destructor performs s = static_cast<Smart>(p);, and the program is ill-formed if sizeof...(Args) > 0;
• otherwise, if s.reset(static_cast<SP>(p), std::forward<Args>(args)...) is well-formed, the destructor performs

/*do-release*/; if (p) { s.reset(static_cast<SP>(p), std::forward<Args>(args)...); };

• otherwise, if std::is_constructible_v<Smart, SP, Args...> is true, the destructor performs

/*do-release*/; if (p) { s = Smart(static_cast<SP>(p), std::forward<Args>(args)...); };

• otherwise, the program is ill-formed.

🚨 Bestie, that last “otherwise” is not a drill: the program is ill-formed. Periodt.

💅 Notes 💅

• The implementation may allocate the storage for the data structure needed for Smart (e.g. a control block) on construction, in order to leave non-throwing works to the destructor. 👀
• Arguments captured by value are destroyed after resetting. 🧼

🩹 Defect reports 🩹

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

• DR: LWG 3897 — Applied to: C++23. Behavior as published: the destructor did not update a raw pointer to the null value. Correct behavior: it does. ✅

Source: http://cppreference.com · Version/date: 2024.06.10 · Page: std::inout_...inout_ptr_t(3) — bye bestie, go destroy responsibly! 💅✨🎀