p-groarke / fea_state_machines

A Buffet Of C++17 State Machines

This repository is inactive and kept for posterity's sake.

Any further development will happen in fea_libs. Cheers.

fea_state_machines

A buffet of state machines.

Available Machines

Each header contains a more detailed explanation of the state machine's features, design and limitations. Here is a quick overview.

fsm.hpp

This is a stack based state machine. It is very fast and supports the most essential fsm features. Under the hood, it uses std::array and std::function. This is a great fsm if you need many machines running concurrently, or you need a very fast runtime machine. The design is very simple, making it robust and easy to debug.

hfsm.hpp

This is the "big boi". A full implementation of a hierarchical finite state machine (aka state chart). It is a heap fsm, evaluation uses a queue to process your events. It has all the bells and whistles : transition guards, auto transition guards, history state, parallel states, parent/children states, etc. Use this for very complex behavior you need to manage.

constexpr_fsm.hpp

This is a compile-time executable state machine. It is mostly a novel design to experiment with the possibilities opened up when creating a truly constexpr state machine. The features are quite limited, though you have the added benefit of compile-time validation. For experimentation only, a thorough deep-dive is available in this blog post.

inlined_fsm

TODO: This will be a mirror state machine to fsm.hpp. It should have a reasonable amount of features, with less overhead using std::tuple and storing your functions directly without the need of std::function or C pointers. If this gains feature parity with fsm.hpp, it will replace it.

Build

fea_state_machines is a header only state machine lib with no dependencies other than the stl.

The unit tests depend on gtest. They are not built by default.

Install recent conan, cmake and compiler.

mkdir build && cd build
cmake .. -DBUILD_TESTING=On && cmake --build . --config debug
bin/fea_state_machines_tests.exe

// Optionally
cmake --build . --target install

fea_state_machines's Issues

Question regarding member function

The machine now supports member function callbacks.
When using member function callbacks, add an object pointer as the first argument to your callback, like you would with std::function.
For example : fea::fsm_builder<my_transitions, my_states, void(MyObj*, bool, int)>
Then, add events using references to your member function pointer : add_event<fsm_event::on_enter>(&MyObj::my_enter_func)

Regarding this:
Before that, I've used member funtions like this:
add_event<fsm_event::on_enter>(std::bind(&MyObj::MyEnterFnc, this, std::placeholders::_1, std::placeholders::_2));

Do you know if there are some performance / memory differences between those two?

potential bug in fsm.hpp

Hey,
first of all great fsm's. I've read your article on isocpp.

If you enable FEA_FSM_NOTHROW the assert statement should be

std::get<size_t(Transition)>(_transitions) != StateEnum::count

or maybe even better with a message?
assert(("fsm_state : unhandled transition", std::get<size_t(Transition)>(_transitions) != StateEnum::count));

https://github.com/p-groarke/fea_state_machines/blob/master/include/fea_state_machines/fsm.hpp#L137