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


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# File 'lib/state_machines/state.rb', line 53

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 && name.to_s
  @cache = options[:cache]
  @matcher = options[:if]
  @initial = options[:initial] == true
  @context = StateContext.new(self)

  if name
    conflicting_machines = machine.owner_class.state_machines.select { |other_name, other_machine| other_machine != machine && other_machine.states[qualified_name, :qualified_name] }

    # Output a warning if another machine has a conflicting qualified name
    # for a different attribute
    if conflict = conflicting_machines.detect { |other_name, other_machine| other_machine.attribute != machine.attribute }
      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
end

Instance Attribute Details

#cacheObject

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


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# File 'lib/state_machines/state.rb', line 30

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”


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# File 'lib/state_machines/state.rb', line 110

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

#initialObject Also known as: initial?

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


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

def initial
  @initial
end

#machineObject

The state machine for which this state is defined


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# File 'lib/state_machines/state.rb', line 13

def machine
  @machine
end

#matcherObject

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


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# File 'lib/state_machines/state.rb', line 38

def matcher
  @matcher
end

#nameObject (readonly)

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


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

def name
  @name
end

#qualified_nameObject (readonly)

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


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# File 'lib/state_machines/state.rb', line 20

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:[email protected]>

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# File 'lib/state_machines/state.rb', line 143

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.


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# File 'lib/state_machines/state.rb', line 219

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 => ex
      if ex.name.to_s == options[:method_name].to_s && ex.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]}")
      else
        raise
      end
    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.


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# File 'lib/state_machines/state.rb', line 181

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.select { |(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_methodsObject

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


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# File 'lib/state_machines/state.rb', line 208

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


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# File 'lib/state_machines/state.rb', line 127

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 = {}) ⇒ Object


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# File 'lib/state_machines/state.rb', line 242

def draw(graph, options = {})
  fail NotImplementedError
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)

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# File 'lib/state_machines/state.rb', line 98

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

#initialize_copy(orig) ⇒ Object

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


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# File 'lib/state_machines/state.rb', line 84

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

#inspectObject

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=[]>

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# File 'lib/state_machines/state.rb', line 252

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)

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# File 'lib/state_machines/state.rb', line 172

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