FFSM: Flat Finite State Machine Framework

Header-only flat FSM framework, made as an example to illustrate twitter thread on #cpp #state_machine #software_design.

Compiler Support

• Visual Studio 14, 15, 16
• GCC 7, 8
• Clang 5, 6, 7

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Basic Usage

1. Include FFSM header:

#include <ffsm/machine.hpp>

2. Define interface class between the state machine and its host (also ok to use the host object itself):

struct Context {
    // ...
};

3. (Optional, recommended) Typedef ffsm::Machine for convenience:

using M = ffsm::Machine<Context>;

4. (Optional) Forward declare transition target states:

struct Second;

5. Define states inheriting them from M::State:

struct First
    : M::State
{
    virtual void update(Control& control) override {
        control.changeTo<Second>();
    }
};

struct Second
    : M::State
{
    virtual void update(Control& control) override {
        control.changeTo<First>();
    }
};

struct Done : M::State {};

6. Declare state machine structure:

using FSM = M::Host<First,
                    Second,
                    Done>;

7. Write the client code to use your new state machine:

int main() {

8. Create context and state machine instances:

    Context context;
    FSM fsm(context);

9. Kick off periodic updates until it's done:

    while (!fsm.isActive<Done>())
        fsm.update();

    return 0;
}

Get Updates

• Original twitter thread on #cpp #state_machine #software_design
• FFSM's "Older sibling" - Hierarchical FSM framework
• Blog
• Twitter