class StateMachine::State

A state defines a value that an attribute can be in after being transitioned 0 or more times. States can represent a value of any type in Ruby, though the most common (and default) type is String.

In addition to defining the machine's value, a state can also define a behavioral context for an object when that object is in the state. See StateMachine::Machine#state for more information about how state-driven behavior can be utilized.

Attributes

cache[RW]

Whether this state's value should be cached after being evaluated

human_name[W]

The human-readable name for the state

initial[RW]

Whether or not this state is the initial state to use for new objects

initial?[RW]

Whether or not this state is the initial state to use for new objects

machine[RW]

The state machine for which this state is defined

matcher[RW]

A custom lambda block for determining whether a given value matches this state

methods[R]

Tracks all of the methods that have been defined for the machine's owner class when objects are in this state.

Maps :method_name => UnboundMethod

name[R]

The unique identifier for the state used in event and callback definitions

qualified_name[R]

The fully-qualified identifier for the state, scoped by the machine's namespace

value[W]

The value that is written to a machine's attribute when an object transitions into this state

Public Instance Methods

call(object, method, method_missing = nil, *args, &block) click to toggle source

Calls a method defined in this state's context on the given object. All arguments and any block will be passed into the method defined.

If the method has never been defined for this state, then a NoMethodError will be raised.

# File lib/state_machine/state.rb, line 216
def call(object, method, method_missing = nil, *args, &block)
  if machine.states.matches?(object, name) && context_method = methods[method.to_sym]
    # Method is defined by the state: proxy it through
    context_method.bind(object).call(*args, &block)
  else
    # Dispatch to the superclass since the object either isn't in this state
    # or this state doesn't handle the method
    method_missing.call if method_missing
  end
end
context(&block) click to toggle source

Defines a context for the state which will be enabled on instances of the owner class when the machine is in this state.

This can be called multiple times. Each time a new context is created, a new module will be included in the owner class.

# File lib/state_machine/state.rb, line 186
    def context(&block)
      machine_name = machine.name
      
      # Evaluate the method definitions
      context = StateContext.new(self)
      context.class_eval(&block)
      context.instance_methods.each do |method|
        methods[method.to_sym] = context.instance_method(method)
        
        # Calls the method defined by the current state of the machine
        context.class_eval "          remove_method :#{method}
          def #{method}(*args, &block)
            self.class.state_machine(#{machine_name.inspect}).states.fetch(#{name.inspect}).call(self, #{method.inspect}, lambda {super(*args, &block)}, *args, &block)
          end
", __FILE__, __LINE__ + 1
      end
      
      # Include the context so that it can be bound to the owner class (the
      # context is considered an ancestor, so it's allowed to be bound)
      machine.owner_class.class_eval { include context }
      
      context
    end
description(options = {}) click to toggle source

Generates a human-readable description of this state's name / value:

For example,

State.new(machine, :parked).description                               # => "parked"
State.new(machine, :parked, :value => :parked).description            # => "parked"
State.new(machine, :parked, :value => nil).description                # => "parked (nil)"
State.new(machine, :parked, :value => 1).description                  # => "parked (1)"
State.new(machine, :parked, :value => lambda {Time.now}).description  # => "parked (*)

Configuration options:

  • :human_name - Whether to use this state's human name in the description or just the internal name

# File lib/state_machine/state.rb, line 132
def description(options = {})
  label = options[:human_name] ? human_name : name
  description = label ? label.to_s : label.inspect
  description << " (#{@value.is_a?(Proc) ? '*' : @value.inspect})" unless name.to_s == @value.to_s
  description
end
draw(graph, options = {}) click to toggle source

Draws a representation of this state on the given machine. This will create a new node on the graph with the following properties:

  • label - The human-friendly description of the state.

  • width - The width of the node. Always 1.

  • height - The height of the node. Always 1.

  • shape - The actual shape of the node. If the state is a final state, then “doublecircle”, otherwise “ellipse”.

Configuration options:

  • :human_name - Whether to use the state's human name for the node's label that gets drawn on the graph

# File lib/state_machine/state.rb, line 238
def draw(graph, options = {})
  node = graph.add_nodes(name ? name.to_s : 'nil',
    :label => description(options),
    :width => '1',
    :height => '1',
    :shape => final? ? 'doublecircle' : 'ellipse'
  )
  
  # Add open arrow for initial state
  graph.add_edges(graph.add_nodes('starting_state', :shape => 'point'), node) if initial?
  
  true
end
final?() click to toggle source

Determines whether there are any states that can be transitioned to from this state. If there are none, then this state is considered final. Any objects in a final state will remain so forever given the current machine's definition.

# File lib/state_machine/state.rb, line 103
def final?
  !machine.events.any? do |event|
    event.branches.any? do |branch|
      branch.state_requirements.any? do |requirement|
        requirement[:from].matches?(name) && !requirement[:to].matches?(name, :from => name)
      end
    end
  end
end
human_name(klass = @machine.owner_class) click to toggle source

Transforms the state name into a more human-readable format, such as “first gear” instead of “first_gear”

# File lib/state_machine/state.rb, line 115
def human_name(klass = @machine.owner_class)
  @human_name.is_a?(Proc) ? @human_name.call(self, klass) : @human_name
end
inspect() click to toggle source

Generates a nicely formatted description of this state's contents.

For example,

state = StateMachine::State.new(machine, :parked, :value => 1, :initial => true)
state   # => #<StateMachine::State name=:parked value=1 initial=true context=[]>
# File lib/state_machine/state.rb, line 258
def inspect
  attributes = [[:name, name], [:value, @value], [:initial, initial?], [:context, methods.keys]]
  "#<#{self.class} #{attributes.map {|attr, value| "#{attr}=#{value.inspect}"} * ' '}>"
end
matches?(other_value) click to toggle source

Determines whether this state matches the given value. If no matcher is configured, then this will check whether the values are equivalent. Otherwise, the matcher will determine the result.

For example,

# Without a matcher
state = State.new(machine, :parked, :value => 1)
state.matches?(1)           # => true
state.matches?(2)           # => false

# With a matcher
state = State.new(machine, :parked, :value => lambda {Time.now}, :if => lambda {|value| !value.nil?})
state.matches?(nil)         # => false
state.matches?(Time.now)    # => true
# File lib/state_machine/state.rb, line 177
def matches?(other_value)
  matcher ? matcher.call(other_value) : other_value == value
end
value(eval = true) click to toggle source

The value that represents this state. This will optionally evaluate the original block if it's a lambda block. Otherwise, the static value is returned.

For example,

State.new(machine, :parked, :value => 1).value                        # => 1
State.new(machine, :parked, :value => lambda {Time.now}).value        # => Tue Jan 01 00:00:00 UTC 2008
State.new(machine, :parked, :value => lambda {Time.now}).value(false) # => <Proc:0xb6ea7ca0@...>
# File lib/state_machine/state.rb, line 148
def value(eval = true)
  if @value.is_a?(Proc) && eval
    if cache_value?
      @value = @value.call
      machine.states.update(self)
      @value
    else
      @value.call
    end
  else
    @value
  end
end

Private Instance Methods

add_predicate() click to toggle source

Adds a predicate method to the owner class so long as a name has actually been configured for the state

# File lib/state_machine/state.rb, line 271
def add_predicate
  # Checks whether the current value matches this state
  machine.define_helper(:instance, "#{qualified_name}?") do |machine, object|
    machine.states.matches?(object, name)
  end
end
cache_value?() click to toggle source

Should the value be cached after it's evaluated for the first time?

# File lib/state_machine/state.rb, line 265
def cache_value?
  @cache
end