fsm's Introduction

Finite State Machine

ecpp::fsm is a finite state machine C++20 (C++17 in C++17 branch) library designed for usage in single threaded environment.

Inspiration and Motivation

The ecpp::fsm library was inspired by ::afsm library and implemented in such a way that it would repeat the syntax of ::afsm as closely as possible. The cpp::fsm library is compiled by any compiler that supports C++20, while ::afsm is not compiled by compilers Microsoft Visual Studio and MinGW.

Features

Statechart features
- Transition actions
- Internal transitions
- Transition guards (conditions)
Compile-time checks
Header only
Relatively fast compile time
No external dependencies

Synopsis

Here is a UML diagram of a trivial state machine and source code that it is mapped to.

#include <cassert>
#include <fsm/fsm_ecpp.h>

using namespace ecpp::fsm;

// Events
struct start {};
struct stop {};

// State machine definition
struct minimal_def {
//@{
/** @name States */
struct initial      : state<initial> {};
struct running      : state<running> {};
struct terminated   : state<terminated> {};
//@}

using initial_state = initial;
using transitions   = transition_table
  <
    /*  State       Event       Next        */
    tr< initial,    start,      running     >,
    tr< running,    stop,       terminated  >
  >;
};

// State machine object
using minimal = ecpp::fsm::state_machine<minimal_def>;

void use()
{
    minimal fsm;
    assert(fsm.is_in_state<minimal_def::initial>());
    assert(fsm.process_event(start{}) == event_result::done);
    assert(fsm.is_in_state<minimal_def::running>());
    assert(fsm.process_event(stop{})  == event_result::done);
    assert(fsm.is_in_state<minimal_def::terminated>());
}