class StateMachine::Callback

Callbacks represent hooks into objects that allow logic to be triggered before, after, or around a specific set of transitions.

Attributes

bind_to_object[RW]

Determines whether to automatically bind the callback to the object being transitioned. This only applies to callbacks that are defined as lambda blocks (or Procs). Some integrations, such as DataMapper, handle callbacks by executing them bound to the object involved, while other integrations, such as ActiveRecord, pass the object as an argument to the callback. This can be configured on an application-wide basis by setting this configuration to true or false. The default value is false.

Note that the DataMapper and Sequel integrations automatically configure this value on a per-callback basis, so it does not have to be enabled application-wide.

Examples

When not bound to the object:

class Vehicle
  state_machine do
    before_transition do |vehicle|
      vehicle.set_alarm
    end
  end

  def set_alarm
    ...
  end
end

When bound to the object:

StateMachine::Callback.bind_to_object = true

class Vehicle
  state_machine do
    before_transition do
      self.set_alarm
    end
  end

  def set_alarm
    ...
  end
end
terminator[RW]

The application-wide terminator to use for callbacks when not explicitly defined. Terminators determine whether to cancel a callback chain based on the return value of the callback.

See #terminator for more information.

branch[R]

The branch that determines whether or not this callback can be invoked based on the context of the transition. The event, from state, and to state must all match in order for the branch to pass.

See StateMachine::Branch for more information.

terminator[R]

An optional block for determining whether to cancel the callback chain based on the return value of the callback. By default, the callback chain never cancels based on the return value (i.e. there is no implicit terminator). Certain integrations, such as ActiveRecord and Sequel, change this default value.

Examples

Canceling the callback chain without a terminator:

class Vehicle
  state_machine do
    before_transition do |vehicle|
      throw :halt
    end
  end
end

Canceling the callback chain with a terminator value of false:

class Vehicle
  state_machine do
    before_transition do |vehicle|
      false
    end
  end
end
type[RW]

The type of callback chain this callback is for. This can be one of the following:

  • before

  • after

  • around

  • failure

Public Class Methods

new(type, *args, &block) click to toggle source

Creates a new callback that can get called based on the configured options.

In addition to the possible configuration options for branches, the following options can be configured:

  • :bind_to_object - Whether to bind the callback to the object involved. If set to false, the object will be passed as a parameter instead. Default is integration-specific or set to the application default.

  • :terminator - A block/proc that determines what callback results should cause the callback chain to halt (if not using the default throw :halt technique).

More information about how those options affect the behavior of the callback can be found in their attribute definitions.

# File lib/state_machine/callback.rb, line 123
def initialize(type, *args, &block)
  @type = type
  raise ArgumentError, 'Type must be :before, :after, :around, or :failure' unless [:before, :after, :around, :failure].include?(type)
  
  options = args.last.is_a?(Hash) ? args.pop : {}
  @methods = args
  @methods.concat(Array(options.delete(:do)))
  @methods << block if block_given?
  raise ArgumentError, 'Method(s) for callback must be specified' unless @methods.any?
  
  options = {:bind_to_object => self.class.bind_to_object, :terminator => self.class.terminator}.merge(options)
  
  # Proxy lambda blocks so that they're bound to the object
  bind_to_object = options.delete(:bind_to_object)
  @methods.map! do |method|
    bind_to_object && method.is_a?(Proc) ? bound_method(method) : method
  end
  
  @terminator = options.delete(:terminator)
  @branch = Branch.new(options)
end

Public Instance Methods

call(object, context = {}, *args, &block) click to toggle source

Runs the callback as long as the transition context matches the branch requirements configured for this callback. If a block is provided, it will be called when the last method has run.

If a terminator has been configured and it matches the result from the evaluated method, then the callback chain should be halted.

# File lib/state_machine/callback.rb, line 157
def call(object, context = {}, *args, &block)
  if @branch.matches?(object, context)
    run_methods(object, context, 0, *args, &block)
    true
  else
    false
  end
end
known_states() click to toggle source

Gets a list of the states known to this callback by looking at the branch's known states

# File lib/state_machine/callback.rb, line 147
def known_states
  branch.known_states
end

Private Instance Methods

bound_method(block) click to toggle source

Generates a method that can be bound to the object being transitioned when the callback is invoked

# File lib/state_machine/callback.rb, line 199
def bound_method(block)
  type = self.type
  arity = block.arity
  arity += 1 if arity >= 0 # Make sure the object gets passed
  arity += 1 if arity == 1 && type == :around  # Make sure the block gets passed
  
  method = if RUBY_VERSION >= '1.9'
    lambda do |object, *args|
      object.instance_exec(*args, &block)
    end
  else
    # Generate a thread-safe unbound method that can be used on any object.
    # This is a workaround for not having Ruby 1.9's instance_exec
    unbound_method = Object.class_eval do
      time = Time.now
      method_name = "__bind_#{time.to_i}_#{time.usec}"
      define_method(method_name, &block)
      method = instance_method(method_name)
      remove_method(method_name)
      method
    end
    
    # Proxy calls to the method so that the method can be bound *and*
    # the arguments are adjusted
    lambda do |object, *args|
      unbound_method.bind(object).call(*args)
    end
  end
  
  # Proxy arity to the original block
  (class << method; self; end).class_eval do
    define_method(:arity) { arity }
  end
  
  method
end
run_methods(object, context = {}, index = 0, *args) { || ... } click to toggle source

Runs all of the methods configured for this callback.

When running around callbacks, this will evaluate each method and yield when the last method has yielded. The callback will only halt if one of the methods does not yield.

For all other types of callbacks, this will evaluate each method in order. The callback will only halt if the resulting value from the method passes the terminator.

# File lib/state_machine/callback.rb, line 176
def run_methods(object, context = {}, index = 0, *args, &block)
  if type == :around
    if current_method = @methods[index]
      yielded = false
      evaluate_method(object, current_method, *args) do
        yielded = true
        run_methods(object, context, index + 1, *args, &block)
      end
      
      throw :halt unless yielded
    else
      yield if block_given?
    end
  else
    @methods.each do |method|
      result = evaluate_method(object, method, *args)
      throw :halt if @terminator && @terminator.call(result)
    end
  end
end