MicroFSM implements a minimal/simple Finite-State Machine (FSM). Transitions are triggered by events. Actions for a transition can be added as callbacks.
Finite-State Machine are described elsewhere, e.g. Wikipedia.
Several FSM implementations are available for Ruby. Please feel free to use any of them if they fit better to your work.
The MicroFSM code consists of less than 100 locs. No magic, no niceties, just an implementation using Ruby hashes.
As usual:
# Gemfile
gem "microfsm"and run "bundle install".
require 'microfsm'
fsm = MicroFSM.new(:new) # Initial state.
# Define the possible transitions for each event.
# Template: fsm.when(<event>, <from> => <to>)
fsm.when(:confirm, new: :confirmed)
fsm.when(:ignore, new: :ignored)
fsm.when(:reset, confirmed: :new, ignored: :new)
fsm.trigger(:confirm) #=> true
fsm.state #=> :confirmed
fsm.trigger(:ignore) #=> false
fsm.state #=> :confirmed
fsm.trigger(:reset) #=> true
fsm.state #=> :new
fsm.trigger(:ignore) #=> true
fsm.state #=> :ignoredYou can also ask if an event will trigger a change in state. Following the example above:
fsm.state #=> :ignored
fsm.trigger?(:ignore) #=> false
fsm.trigger?(:reset) #=> true
# And the state is preserved, because you were only asking.
fsm.state #=> :ignoredAdding actions to a transition is trivial:
fsm.when(:confirm, new: :confirmed) { |event| count += 1 }
fsm.when(:confirm, new: :confirmed) { |event| foo(event) }Two actions/callbacks are triggered in the previous example.
Finally, you can list possible events or states:
# All possible events
fsm.events #=> [:confirm, :ignore, :reset]
# All events triggerable from the current state
fsm.triggerable_events #=> [:confirm, :ignore]
# All possible states
fsm.states #=> [:new, :confirmed, :ignored]And, the state can be set (which may be useful for testing purposes):
fsm.state = :new
fsm.state #=> :newCheck the examples directory for more information.
Copyright (c) 2021-2025 Dittmar Krall (www.matiq.com), released under the MIT license.