unmanaged_storage.hpp

// The UnmanagedStorage wrapper is used to disable dynamic initialization and
// destructor calls for global variables. The wrapped object is stored inline
// and needs to be created and destroyed manually.
template <typename T>
class UnmanagedStorage {
  public:
	template <typename... Args>
	T* emplace(Args&&... args) noexcept
	{
		reset();
		new (m_instance) T(std::forward<Args>(args)...);
		m_hasInstance = true;
		return get();
	}

	void reset() noexcept
	{
		if (m_hasInstance) {
			m_hasInstance = false;
			get()->~T();
		}
	}

	T* get() noexcept
	{
		if (!m_hasInstance) [[unlikely]] {
			return nullptr;
		}
		return reinterpret_cast<T*>(&m_instance);
	}
	const T* get() const noexcept { const_cast<UnmanagedStorage<T>*>(this)->get(); }

	T* operator->() noexcept { return get(); }
	const T* operator->() const noexcept { return get(); }

	explicit operator bool() const { return m_hasInstance; }

  private:
	bool m_hasInstance = false;
	alignas(T) uint8_t m_instance[sizeof(T)] = {};
};