Class: StateMachine::StateContext

Inherits:
Module
  • Object
show all
Includes:
Assertions, EvalHelpers
Defined in:
lib/state_machine/state_context.rb

Overview

Represents a module which will get evaluated within the context of a state.

Class-level methods are proxied to the owner class, injecting a custom :if condition along with method. This assumes that the method has support for a set of configuration options, including :if. This condition will check that the object's state matches this context's state.

Instance-level methods are used to define state-driven behavior on the state's owner class.

Examples

class Vehicle
  class << self
    attr_accessor :validations

    def validate(options, &block)
      validations << options
    end
  end

  self.validations = []
  attr_accessor :state, :simulate

  def moving?
    self.class.validations.all? {|validation| validation[:if].call(self)}
  end
end

In the above class, a simple set of validation behaviors have been defined. Each validation consists of a configuration like so:

Vehicle.validate :unless => :simulate
Vehicle.validate :if => lambda {|vehicle| ...}

In order to scope validations to a particular state context, the class-level validate method can be invoked like so:

machine = StateMachine::Machine.new(Vehicle)
context = StateMachine::StateContext.new(machine.state(:first_gear))
context.validate(:unless => :simulate)

vehicle = Vehicle.new     # => #<Vehicle:0xb7ce491c @simulate=nil, @state=nil>
vehicle.moving?           # => false

vehicle.state = 'first_gear'
vehicle.moving?           # => true

vehicle.simulate = true
vehicle.moving?           # => false

Instance Attribute Summary (collapse)

Instance Method Summary (collapse)

Methods included from EvalHelpers

#evaluate_method

Methods included from Assertions

#assert_exclusive_keys, #assert_valid_keys

Constructor Details

- (StateContext) initialize(state)

Creates a new context for the given state



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# File 'lib/state_machine/state_context.rb', line 66

def initialize(state)
  @state = state
  @machine = state.machine
  
  state_name = state.name
  machine_name = machine.name
  @condition = lambda {|object| object.class.state_machine(machine_name).states.matches?(object, state_name)}
end

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

- (Object) method_missing(*args, &block)

Hooks in condition-merging to methods that don't exist in this module



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# File 'lib/state_machine/state_context.rb', line 100

def method_missing(*args, &block)
  # Get the configuration
  if args.last.is_a?(Hash)
    options = args.last
  else
    args << options = {}
  end
  
  # Get any existing condition that may need to be merged
  if_condition = options.delete(:if)
  unless_condition = options.delete(:unless)
  
  # Provide scope access to configuration in case the block is evaluated
  # within the object instance
  proxy = self
  proxy_condition = @condition
  
  # Replace the configuration condition with the one configured for this
  # proxy, merging together any existing conditions
  options[:if] = lambda do |*args|
    # Block may be executed within the context of the actual object, so
    # it'll either be the first argument or the executing context
    object = args.first || self
    
    proxy.evaluate_method(object, proxy_condition) &&
    Array(if_condition).all? {|condition| proxy.evaluate_method(object, condition)} &&
    !Array(unless_condition).any? {|condition| proxy.evaluate_method(object, condition)}
  end
  
  # Evaluate the method on the owner class with the condition proxied
  # through
  machine.owner_class.send(*args, &block)
end

Instance Attribute Details

- (Object) machine (readonly)

The state machine for which this context's state is defined



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# File 'lib/state_machine/state_context.rb', line 60

def machine
  @machine
end

- (Object) state (readonly)

The state that must be present in an object for this context to be active



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# File 'lib/state_machine/state_context.rb', line 63

def state
  @state
end

Instance Method Details

- (Object) transition(options)

Creates a new transition that determines what to change the current state to when an event fires from this state.

Since this transition is being defined within a state context, you do not need to specify the :from option for the transition. For example:

state_machine do
  state :parked do
    transition :to => :idling, :on => [:ignite, :shift_up]                          # Transitions to :idling
    transition :from => [:idling, :parked], :on => :park, :unless => :seatbelt_on?  # Transitions to :parked if seatbelt is off
  end
end

See StateMachine::Machine#transition for a description of the possible configurations for defining transitions.

Raises:

  • (ArgumentError)


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# File 'lib/state_machine/state_context.rb', line 91

def transition(options)
  assert_valid_keys(options, :from, :to, :on, :if, :unless)
  raise ArgumentError, 'Must specify :on event' unless options[:on]
  raise ArgumentError, 'Must specify either :to or :from state' unless !options[:to] ^ !options[:from]
  
  machine.transition(options.merge(options[:to] ? {:from => state.name} : {:to => state.name}))
end