instance method association_constructor_method

# File activerecord/lib/active_record/associations.rb, line 1402
        def association_constructor_method(constructor, reflection, association_proxy_class)
          define_method("#{constructor}_#{reflection.name}") do |*params|
            ivar = "@#{reflection.name}"

            attributees      = params.first unless params.empty?
            replace_existing = params[1].nil? ? true : params[1]
            association      = instance_variable_get(ivar) if instance_variable_defined?(ivar)

            if association.nil?
              association = association_proxy_class.new(self, reflection)
              instance_variable_set(ivar, association)
            end

            if association_proxy_class == HasOneAssociation
              association.send(constructor, attributees, replace_existing)
            else
              association.send(constructor, attributees)
            end
          end
        end