define_callback

# File activerecord/lib/active_record/associations/builder/collection_association.rb, line 30
    def self.define_callback(model, callback_name, name, options)
      full_callback_name = "#{callback_name}_for_#{name}"

      unless model.method_defined?(full_callback_name)
        model.class_attribute(full_callback_name, instance_accessor: false, instance_predicate: false)
      end

      callbacks = Array(options[callback_name.to_sym]).map do |callback|
        case callback
        when Symbol
          ->(method, owner, record) { owner.send(callback, record) }
        when Proc
          ->(method, owner, record) { callback.call(owner, record) }
        else
          ->(method, owner, record) { callback.send(method, owner, record) }
        end
      end
      model.send "#{full_callback_name}=", callbacks
    end