fsmlite
fsmlite is a lightweight finite state machine framework for C++11. It is based on concepts first presented by David Abrahams and Aleksey Gurtovoy in C++ Template Metaprogramming, with additional ideas taken liberally from Boost's Meta State Machine (MSM).
The canonical CD player example (with CD-Text and auto-play support!) therefore looks somewhat like this:
#include "fsm.h"
#include <string>
class player: public fsmlite::fsm<player> {
// grant base class access to private transition_table
friend class fsmlite::fsm<player>;
std::string cd_title;
bool autoplay = false;
public:
enum states { Stopped, Open, Empty, Playing, Paused };
player(state_type init_state = Empty) : fsm(init_state) { }
void set_autoplay(bool f) { autoplay = f; }
bool is_autoplay() const { return autoplay; }
const std::string& get_cd_title() const { return cd_title; }
struct play {};
struct open_close {};
struct cd_detected { std::string title; };
struct stop {};
struct pause {};
private:
// guards
bool is_autoplay(const cd_detected&) const { return autoplay; }
bool is_bad_cd(const cd_detected& cd) const { return cd.title.empty(); }
// actions
void start_playback(const play&);
void start_autoplay(const cd_detected& cd);
void open_drawer(const open_close&);
void open_drawer(const cd_detected& cd);
void close_drawer(const open_close&);
void store_cd_info(const cd_detected& cd);
void stop_playback(const stop&);
void pause_playback(const pause&);
void stop_and_open(const open_close&);
void resume_playback(const play&);
private:
using m = player; // for brevity
using transition_table = table<
// Start Event Target Action Guard (optional)
// -----------+--------+------------+--------+-------------------+---------------+-
mem_fn_row< Stopped, play, Playing, &m::start_playback >,
mem_fn_row< Stopped, open_close, Open, &m::open_drawer >,
mem_fn_row< Open, open_close, Empty, &m::close_drawer >,
mem_fn_row< Empty, open_close, Open, &m::open_drawer >,
mem_fn_row< Empty, cd_detected, Open, &m::open_drawer, &m::is_bad_cd >,
mem_fn_row< Empty, cd_detected, Playing, &m::start_autoplay, &m::is_autoplay >,
mem_fn_row< Empty, cd_detected, Stopped, &m::store_cd_info /* fallback */ >,
mem_fn_row< Playing, stop, Stopped, &m::stop_playback >,
mem_fn_row< Playing, pause, Paused, &m::pause_playback >,
mem_fn_row< Playing, open_close, Open, &m::stop_and_open >,
mem_fn_row< Paused, play, Playing, &m::resume_playback >,
mem_fn_row< Paused, stop, Stopped, &m::stop_playback >,
mem_fn_row< Paused, open_close, Open, &m::stop_and_open >
// -----------+--------+------------+--------+-------------------+---------------+-
>;
};
C++17 will give you a little more flexibility:
class player: public fsmlite::fsm<player> {
// grant base class access to private transition_table
friend class fsmlite::fsm<player>;
std::string cd_title;
bool autoplay = false;
public:
enum states { Stopped, Open, Empty, Playing, Paused };
player(state_type init_state = Empty) : fsm(init_state) { }
void set_autoplay(bool f) { autoplay = f; }
bool is_autoplay() const { return autoplay; }
const std::string& get_cd_title() const { return cd_title; }
struct play {};
struct open_close {};
struct cd_detected {
std::string title;
bool bad() const { return title.empty(); }
};
struct stop {};
struct pause {};
private:
void start_playback();
void start_autoplay(const cd_detected& cd);
void open_drawer();
void close_drawer();
void store_cd_info(const cd_detected& cd);
void stop_playback();
void pause_playback();
void resume_playback();
void stop_and_open();
private:
using m = player; // for brevity
using transition_table = table<
// Start Event Target Action Guard (optional)
// ----+--------+------------+--------+-------------------+-----------------+-
row< Stopped, play, Playing, &m::start_playback >,
row< Stopped, open_close, Open, &m::open_drawer >,
row< Open, open_close, Empty, &m::close_drawer >,
row< Empty, open_close, Open, &m::open_drawer >,
row< Empty, cd_detected, Open, &m::open_drawer, &cd_detected::bad >,
row< Empty, cd_detected, Playing, &m::start_autoplay, &m::is_autoplay >,
row< Empty, cd_detected, Stopped, &m::store_cd_info /* fallback */ >,
row< Playing, stop, Stopped, &m::stop_playback >,
row< Playing, pause, Paused, &m::pause_playback >,
row< Playing, open_close, Open, &m::stop_and_open >,
row< Paused, play, Playing, &m::resume_playback >,
row< Paused, stop, Stopped, &m::stop_playback >,
row< Paused, open_close, Open, &m::stop_and_open >
// ----+--------+------------+--------+-------------------+-----------------+-
>;
};
Documentation is in the works. In the mean time, please have a look at the unit tests for example usage.
License
Copyright (c) 2015-2021 Thomas Kemmer
Licensed under the MIT License (MIT).