finalizer.h

//-------------------------------------------------------------------
// Provides a "finally" lambda block for C++.
// Example:
// 
// void ReenterableFunction() {
//		static bool isActive = true;                        // static reenterability flag 
//
//		if (isActive) return;                               // check the flag
//		auto reset = finally([&]{ isActive = false; });     // we need to reset the flag on exit, even if there was an exception in the code below.
//		isActive = true;                                    // set the flag and proceed
//
//		// ... do your job here ..
//
//	} // here the flag will be automatically reset
//
//
template <typename F>
struct finalizer
{
	// move constructor
	template<typename T>
	finalizer(T&& finalize) : _finalize(std::forward<T>(finalize)), _armed(true) {
	}
	// old-style move constructor
	finalizer(finalizer&& other) : _finalize(std::move(other._finalize)), _armed(other._armed) {
		other.disarm();
	}
	~finalizer() {
		if (_armed) _finalize();
	}
	void disarm() { 
		_armed = false;
	}
private:
	F _finalize;
	bool _armed;
};

template <typename F>
finalizer<F> finally(F&& finalize) {
   return finalizer<F>(std::forward<F>(finalize));
}