<a href="http://www.boost.org/LICENSE_1_0.txt" target="_blank"></a> <a href="https://github.com/boost-ext/sml/releases" target="_blank"> Version </a> <a href="https://github.com/boost-ext/sml/actions/workflows/build_matrix.yml" target="_blank"></a> <a href="https://codecov.io/gh/boost-ext/sml" target="_blank"></a> <a href="https://godbolt.org/z/y99L50"></a>

SML (State Machine Language)

Your scalable C++14 one header only State Machine Library with no dependencies

https://www.youtube.com/watch?v=Zb6xcd2as6o

Let's release a TCP connection! <img src="doc/images/tcp_release.png" alt="tcp release"/>

Quick start

Download

[Boost::ext].SML requires only one file. Get the latest header here!

Include

#include <boost/sml.hpp>
namespace sml = boost::sml;

Dependencies

struct sender {
  template<class TMsg>
  constexpr void send(const TMsg& msg) { std::printf("send: %d\n", msg.id); }
};

Events

struct ack { bool valid{}; };
struct fin { int id{}; bool valid{}; };
struct release {};
struct timeout {};

Guards

constexpr auto is_valid = [](const auto& event) { return event.valid; };

Actions

constexpr auto send_fin = [](sender& s) { s.send(fin{0}); };
constexpr auto send_ack = [](const auto& event, sender& s) { s.send(event); };

State Machine

struct tcp_release {
  auto operator()() const {
    using namespace sml;
    /**
     * Initial state: *initial_state
     * Transition DSL: src_state + event [ guard ] / action = dst_state
     */
    return make_transition_table(
      *"established"_s + event<release>          / send_fin  = "fin wait 1"_s,
       "fin wait 1"_s  + event<ack> [ is_valid ]             = "fin wait 2"_s,
       "fin wait 2"_s  + event<fin> [ is_valid ] / send_ack  = "timed wait"_s,
       "timed wait"_s  + event<timeout>                      = X
    );
  }
};

Usage

int main() {
  using namespace sml;

  sender s{};
  sm<tcp_release> sm{s}; // pass dependencies via ctor
  assert(sm.is("established"_s));

  sm.process_event(release{}); // complexity O(1)
  assert(sm.is("fin wait 1"_s));

  sm.process_event(ack{true}); // prints 'send: 0'
  assert(sm.is("fin wait 2"_s));

  sm.process_event(fin{42, true}); // prints 'send: 42'
  assert(sm.is("timed wait"_s));

  sm.process_event(timeout{});
  assert(sm.is(X));  // terminated
}

MSVC-2015 (Example)

use state<class state_name> instead of "state_name"_s
expliclty state a lambda's result type auto action = [] -> void {}

Compile

GCC/Clang

$CXX -std=c++14 -O2 -fno-exceptions -Wall -Wextra -Werror -pedantic tcp_release.cpp

MSVC
```
cl /std:c++14 /Ox /W3 tcp_release.cpp
```

<table> <tr> <th>tcp_release.cpp</th> <th>Clang-3.8</th> <th>GCC-6.3</th> <th>MSVC-2015</th> </tr> <tr> <td>Compilation Time</td> <td>0.102s</td> <td>0.118s</td> <td>0.296s</td> </tr> <tr> <td>Binary size (stripped)</td> <td>6.2kb</td> <td>6.2kb</td> <td>105kb</td> </tr> <tr> <td>ASM x86-64 - https://godbolt.org/z/y99L50</td> <td colspan="3"> <pre><code> main: # @main pushq %rax movl $.L.str, %edi xorl %esi, %esi xorl %eax, %eax callq printf movl $.L.str, %edi movl $42, %esi xorl %eax, %eax callq printf xorl %eax, %eax popq %rcx retq .L.str: .asciz "send: %d\n" </code></pre> </td> </tr> </table>

Run

Output (https://wandbox.org/permlink/WbvV9HsIyiPkCFw7)

send: 0
send: 42

Benchmark

Complex Test

| |Enum/Switch | Variant | [Boost::ext].SML - 1.1.0 | Boost-1.65.MSM-eUML | Boost-1.65.Statechart | |------------------|------------|---------|--------------|------------------|--------------------| | Compilation time | 0.132s | 15.321s | 0.582s | 1m15.935s | 5.671s | | Execution time | 679ms | 827ms | 622ms | 664ms | 2282ms | | Memory usage | 1b | 2b/8b | 1b | 120b | 224b | | Executable size | 15K | 187K | 34K | 611K | 211K |

Examples

Arduino

https://godbolt.org/z/Y983h4

https://www.tinkercad.com/things/9epUrFrzKP3

https://godbolt.org/z/qhx8Md

Match3

https://github.com/modern-cpp-examples/match3

Documentation

Introduction
Overview
Features/Benchmarks
- Features
- Benchmarks
Tutorial/Workshop
- 0. Read Boost.MSM - eUML documentation
- 1. Create events and states
- 2. Create guards and actions
- 3. Create a transition table
- 4. Set initial states
- [5. Create a state machine](https://boost-ext.github.io/sml/tutorial.html#5-c

Sml

Install / Use

README