Callbacks are code hooks that are run at key points in an object’s lifecycle. The typical use case is to have a base class define a set of callbacks relevant to the other functionality it supplies, so that subclasses can install callbacks that enhance or modify the base functionality without needing to override or redefine methods of the base class.
Mixing in this module allows you to define the events in the object’s lifecycle that will support callbacks (via ClassMethods.define_callbacks), set the instance methods, procs, or callback objects to be called (via ClassMethods.set_callback), and run the installed callbacks at the appropriate times (via run_callbacks).
Three kinds of callbacks are supported: before callbacks, run before a certain event; after callbacks, run after the event; and around callbacks, blocks that surround the event, triggering it when they yield. Callback code can be contained in instance methods, procs or lambdas, or callback objects that respond to certain predetermined methods. See ClassMethods.set_callback for details.
class Record include ActiveSupport::Callbacks define_callbacks :save def save run_callbacks :save do puts "- save" end end end class PersonRecord < Record set_callback :save, :before, :saving_message def saving_message puts "saving..." end set_callback :save, :after do |object| puts "saved" end end person = PersonRecord.new person.save
saving... - save saved