class StateMachine::Callback
Callbacks represent hooks into objects that allow logic to be triggered before, after, or around a specific set of transitions.
Attributes
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
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.
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.
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
The type of callback chain this callback is for. This can be one of the following:
-
before
-
after
-
around
-
failure
Public Class Methods
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 defaultthrow :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
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
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
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
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