Class: StateMachines::State

Inherits:
Object
  • Object
show all
Defined in:
lib/state_machines/state.rb

Overview

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 StateMachines::Machine#state for more information about how state-driven behavior can be utilized.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(machine, name, options = {}) ⇒ State

Creates a new state within the context of the given machine.

Configuration options:

  • :initial - Whether this state is the beginning state for the machine. Default is false.

  • :value - The value to store when an object transitions to this state. Default is the name (stringified).

  • :cache - If a dynamic value (via a lambda block) is being used, then setting this to true will cache the evaluated result

  • :if - Determines whether a value matches this state (e.g. :value => lambda Time.now, :if => lambda {|state| !state.nil?}). By default, the configured value is matched.

  • :human_name - The human-readable version of this state’s name



54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
 
# File 'lib/state_machines/state.rb', line 54

def initialize(machine, name, options = {}) # :nodoc:
  options.assert_valid_keys(:initial, :value, :cache, :if, :human_name)

  @machine = machine
  @name = name
  @qualified_name = name && machine.namespace ? :"#{machine.namespace}_#{name}" : name
  @human_name = options[:human_name] || (@name ? @name.to_s.tr('_', ' ') : 'nil')
  @value = options.include?(:value) ? options[:value] : name&.to_s
  @cache = options[:cache]
  @matcher = options[:if]
  @initial = options[:initial] == true
  @context = StateContext.new(self)

  return unless name

  conflicting_machines = machine.owner_class.state_machines.select do |_other_name, other_machine|
    other_machine != machine && other_machine.states[qualified_name, :qualified_name]
  end

  # Output a warning if another machine has a conflicting qualified name
  # for a different attribute
  if (conflict = conflicting_machines.detect do |_other_name, other_machine|
    other_machine.attribute != machine.attribute
  end)
    _name, other_machine = conflict
    warn "State #{qualified_name.inspect} for #{machine.name.inspect} is already defined in #{other_machine.name.inspect}"
  elsif conflicting_machines.empty?
    # Only bother adding predicates when another machine for the same
    # attribute hasn't already done so
    add_predicate
  end
end

Instance Attribute Details

#cache ⇒ Object

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



31
32
33
 
# File 'lib/state_machines/state.rb', line 31

def cache
  @cache
end

#human_name(klass = @machine.owner_class) ⇒ Object

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



115
116
117
 
# File 'lib/state_machines/state.rb', line 115

def human_name(klass = @machine.owner_class)
  @human_name.is_a?(Proc) ? @human_name.call(self, klass) : @human_name
end

#initial ⇒ Object Also known as: initial?

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



34
35
36
 
# File 'lib/state_machines/state.rb', line 34

def initial
  @initial
end

#machine ⇒ Object

The state machine for which this state is defined



14
15
16
 
# File 'lib/state_machines/state.rb', line 14

def machine
  @machine
end

#matcher ⇒ Object

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



39
40
41
 
# File 'lib/state_machines/state.rb', line 39

def matcher
  @matcher
end

#name ⇒ Object (readonly)

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



17
18
19
 
# File 'lib/state_machines/state.rb', line 17

def name
  @name
end

#qualified_name ⇒ Object (readonly)

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



21
22
23
 
# File 'lib/state_machines/state.rb', line 21

def qualified_name
  @qualified_name
end

#value(eval = true) ⇒ Object

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@...>



148
149
150
151
152
153
154
155
156
157
158
159
160
 
# File 'lib/state_machines/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

Instance Method Details

#call(object, method, *args, &block) ⇒ Object

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.



224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
 
# File 'lib/state_machines/state.rb', line 224

def call(object, method, *args, &block)
  options = args.last.is_a?(Hash) ? args.pop : {}
  options = { method_name: method }.merge(options)
  state = machine.states.match!(object)

  if state == self && object.respond_to?(method)
    object.send(method, *args, &block)
  elsif (method_missing = options[:method_missing])
    # Dispatch to the superclass since the object either isn't in this state
    # or this state doesn't handle the method
    begin
      method_missing.call
    rescue NoMethodError => e
      raise unless e.name.to_s == options[:method_name].to_s && e.args == args

      # No valid context for this method
      raise InvalidContext.new(object,
                               "State #{state.name.inspect} for #{machine.name.inspect} is not a valid context for calling ##{options[:method_name]}")
    end
  end
end

#context(&block) ⇒ Object

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.



186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
 
# File 'lib/state_machines/state.rb', line 186

def context(&block)
  # Include the context
  context = @context
  machine.owner_class.class_eval { include context }

  # Evaluate the method definitions and track which ones were added
  old_methods = context_methods
  context.class_eval(&block)
  new_methods = context_methods.to_a.reject { |(name, method)| old_methods[name] == method }

  # Alias new methods so that the only execute when the object is in this state
  new_methods.each do |(method_name, _method)|
    context_name = context_name_for(method_name)
    context.class_eval <<-END_EVAL, __FILE__, __LINE__ + 1
      alias_method :"#{context_name}", :#{method_name}
      def #{method_name}(*args, &block)
        state = self.class.state_machine(#{machine.name.inspect}).states.fetch(#{name.inspect})
        options = {:method_missing => lambda {super(*args, &block)}, :method_name => #{method_name.inspect}}
        state.call(self, :"#{context_name}", *(args + [options]), &block)
      end
    END_EVAL
  end

  true
end

#context_methods ⇒ Object

The list of methods that have been defined in this state’s context



213
214
215
216
217
 
# File 'lib/state_machines/state.rb', line 213

def context_methods
  @context.instance_methods.inject({}) do |methods, name|
    methods.merge(name.to_sym => @context.instance_method(name))
  end
end

#description(options = {}) ⇒ Object

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



132
133
134
135
136
137
 
# File 'lib/state_machines/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 = {}, io = $stdout) ⇒ Object 



246
247
248
 
# File 'lib/state_machines/state.rb', line 246

def draw(graph, options = {}, io = $stdout)
  machine.renderer.draw_state(self, graph, options, io)
end

#final? ⇒ Boolean

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.

Returns:

  • (Boolean) 


103
104
105
106
107
108
109
110
111
 
# File 'lib/state_machines/state.rb', line 103

def final?
  machine.events.none? 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

#initialize_copy(orig) ⇒ Object

Creates a copy of this state, excluding the context to prevent conflicts across different machines.



89
90
91
92
 
# File 'lib/state_machines/state.rb', line 89

def initialize_copy(orig) # :nodoc:
  super
  @context = StateContext.new(self)
end

#inspect ⇒ Object

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

For example,

state = StateMachines::State.new(machine, :parked, :value => 1, :initial => true)
state   # => #<StateMachines::State name=:parked value=1 initial=true context=[]>



256
257
258
259
 
# File 'lib/state_machines/state.rb', line 256

def inspect
  attributes = [[:name, name], [:value, @value], [:initial, initial?]]
  "#<#{self.class} #{attributes.map { |attr, value| "#{attr}=#{value.inspect}" } * ' '}>"
end

#matches?(other_value) ⇒ Boolean

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

Returns:

  • (Boolean) 


177
178
179
 
# File 'lib/state_machines/state.rb', line 177

def matches?(other_value)
  matcher ? matcher.call(other_value) : other_value == value
end