repos/Callback_06/Callback_06.cpp

/**
 * Example code for:
 *   - callback storage with std::vector
 *   - use of std::function
 *   - use of std::bind
 *   - use of lambda function as callback
 */

#include <cstdint>
#include <cstdio>
#include <functional>
#include <vector>

 /**
  * Basic std::function callback example. Templated on a function signature
  * that takes in a uint32_t and returns void.
  */
typedef std::function<void(uint32_t)> cb_t;

/**
 * Here's an example type that stores a std::function and an argument
 * to pass with that callback.  Passing a uint32_t input to your callback
 * is a pretty common implementation. Also useful if you need to store a
 * pointer for use with a BOUNCE function.
 */
struct cb_arg_t
{
	// the callback - takes a uint32_t input.
	std::function<void(uint32_t)> cb;
	// value to return with the callback.
	uint32_t arg;
};

/**
 * Alternative storage implementation.  Perhaps you want to store
 * callbacks for different event types?
 */
enum my_events_t
{
	VIDEO_STOP = 0,
	VIDEO_START,
	EVENT_MAX
};

struct cb_event_t
{
	std::function<void(uint32_t)> cb;
	my_events_t event;
};

/**
 * Basic example.  Constructed with a uint32_t.
 * Callbacks are passed this uint32_t.
 */
class BasicDriver
{
public:
	BasicDriver(uint32_t val) : val_(val), callbacks_()
	{
	}

	// Register a callback.
	void register_callback(const cb_t& cb)
	{
		// add callback to end of callback list
		callbacks_.push_back(cb);
	}

	/// Call all the registered callbacks.
	void callback() const
	{
		// iterate through callback list and call each one
		for (const auto& cb : callbacks_)
		{
			cb(val_);
		}
	}

private:
	/// Integer to pass to callbacks.
	uint32_t val_;
	/// List of callback functions.
	std::vector<cb_t> callbacks_;
};

/**
 * Event based example.  Constructed with a uint32_t.
 * Callbacks are passed this uint32_t.
 * Callbacks are only invoked when their event type matches the
 * occuring event.
 */
class EventDriver
{
public:
	EventDriver(uint32_t val) : val_(val), callbacks_()
	{
	}

	// Register a callback.
	void register_callback(const cb_t& cb, const my_events_t event)
	{
		// add callback to end of callback list
		callbacks_.push_back({ cb, event });
	}

	/// Call all the registered callbacks.
	void callback() const
	{
		my_events_t event = VIDEO_START;
		// iterate through callback list and call each one
		for (const auto& cb : callbacks_)
		{
			if (cb.event == event)
			{
				cb.cb(val_);
			}
		}
	}

private:
	/// Integer to pass to callbacks.
	uint32_t val_;
	/// List of callback functions.
	std::vector<cb_event_t> callbacks_;
};

/**
 * Arg based example.
 * Callbacks register with a uint32_t that they want returned
 * Callbacks always passed their specific uint32_t value
 */
class ArgDriver
{
public:
	ArgDriver() : callbacks_()
	{
	}

	// Register a callback.
	void register_callback(const cb_t& cb, const uint32_t val)
	{
		// add callback to end of callback list
		callbacks_.push_back({ cb, val });
	}

	/// Call all the registered callbacks.
	void callback() const
	{
		// iterate through callback list and call each one
		for (const auto& cb : callbacks_)
		{
			cb.cb(cb.arg);
		}
	}

private:
	/// List of callback functions.
	std::vector<cb_arg_t> callbacks_;
};

/**
 * Dummy Client #1
 * Uses a static method for a callback.
 */
class Client1
{
public:
	static void func(uint32_t v)
	{
		printf("static member callback: 0x%x\n", v);
	}
};

/**
 * Dummy Client #2
 * Uses an instance method as a callback
 */
class Client2
{
public:
	void func(uint32_t v) const
	{
		printf("instance member callback: 0x%x\n", v);
	}
};

/**
 * Callback on a c function
 */
extern "C"
{
	static void c_client_callback(uint32_t v)
	{
		printf("C function callback: 0x%x\n", v);
	}
}

int main()
{
	/**
	 * Examples using the basic driver
	 * This is constructed with a specific value
	 * Each callback receives this value
	 */
	BasicDriver bd(0xDEADBEEF); // create basic driver instance
	Client2 c2;

	printf("Starting examples using the BasicDriver\n");
	// register a lambda function as a callback
	bd.register_callback([](uint32_t v) {
		printf("lambda callback: 0x%x\n", v);
		});

	/**
	 * std::bind is used to create a function object using
	 * both the instance and method pointers.  This gives you the
	 * callback into the specific object - very useful!
	 *
	 * std::bind keeps specific arguments at a fixed value (or a placeholder)
	 * For our argument here, we keep as a placeholder.
	 */
	bd.register_callback(std::bind(&Client2::func, &c2, std::placeholders::_1));

	// register a static class method as a callback
	bd.register_callback(&Client1::func);

	// register a C function pointer as a callback
	bd.register_callback(&c_client_callback);

	// call all the registered callbacks
	bd.callback();

	printf("End of examples using the BasicDriver\n");

	/**
	 * Examples using the Event Driver.
	 * Note that some callbacks will not be called -
	 * their event type is different!
	 */
	EventDriver ed(0xFEEDBEEF);

	printf("Beginning of examples using the EventDriver\n");

	// register a lambda function as a callback
	ed.register_callback(
		[](uint32_t v) {
			printf("lambda callback: 0x%x\n", v);
		},
		VIDEO_START);

	// register client2 cb using std::bind
	ed.register_callback(std::bind(&Client2::func, &c2, std::placeholders::_1), VIDEO_STOP);

	// register a static class method as a callback
	ed.register_callback(&Client1::func, VIDEO_STOP);

	// register a C function pointer as a callback
	ed.register_callback(&c_client_callback, VIDEO_START);

	// call all the registered callbacks
	ed.callback();

	printf("End of examples using the EventDriver\n");

	/**
	 * Examples using the Arg Driver.
	 * Note that each callback registers for its own value
	 */
	ArgDriver ad;

	printf("Beginning of examples using the ArgDriver\n");

	// register a lambda function as a callback
	ad.register_callback(
		[](uint32_t v) {
			printf("lambda callback: 0x%x\n", v);
		},
		0x0);

	// register client2 cb using std::bind
	ad.register_callback(std::bind(&Client2::func, &c2, std::placeholders::_1), 0x1);

	// register a static class method as a callback
	ad.register_callback(&Client1::func, 0x2);

	// register a C function pointer as a callback
	ad.register_callback(&c_client_callback, 0x3);

	// call all the registered callbacks
	ad.callback();

	printf("End of examples using the ArgDriver\n");

	return 0;
}