module ActiveSupport::Concern
A typical module looks like this:
module M def self.included(base) base.extend ClassMethods base.send(:include, InstanceMethods) scope :disabled, where(:disabled => true) end module ClassMethods ... end module InstanceMethods ... end end
By using ActiveSupport::Concern
the above module could instead be written as:
require 'active_support/concern' module M extend ActiveSupport::Concern included do scope :disabled, where(:disabled => true) end module ClassMethods ... end module InstanceMethods ... end end
Moreover, it gracefully handles module dependencies. Given a Foo
module and a Bar
module which depends on the former, we would typically write the following:
module Foo def self.included(base) base.class_eval do def self.method_injected_by_foo ... end end end end module Bar def self.included(base) base.method_injected_by_foo end end class Host include Foo # We need to include this dependency for Bar include Bar # Bar is the module that Host really needs end
But why should Host
care about Bar
's dependencies, namely Foo
? We could try to hide these from Host
directly including Foo
in Bar
:
module Bar include Foo def self.included(base) base.method_injected_by_foo end end class Host include Bar end
Unfortunately this won't work, since when Foo
is included, its base
is the Bar
module, not the Host
class. With ActiveSupport::Concern
, module dependencies are properly resolved:
require 'active_support/concern' module Foo extend ActiveSupport::Concern included do class_eval do def self.method_injected_by_foo ... end end end end module Bar extend ActiveSupport::Concern include Foo included do self.method_injected_by_foo end end class Host include Bar # works, Bar takes care now of its dependencies end
Public Class Methods
extended(base)
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# File lib/rails_core_extensions/active_support_concern.rb, line 108 def self.extended(base) base.instance_variable_set("@_dependencies", []) end
Public Instance Methods
append_features(base)
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Calls superclass method
# File lib/rails_core_extensions/active_support_concern.rb, line 112 def append_features(base) if base.instance_variable_defined?("@_dependencies") base.instance_variable_get("@_dependencies") << self return false else return false if base < self @_dependencies.each { |dep| base.send(:include, dep) } super base.extend const_get("ClassMethods") if const_defined?("ClassMethods") base.send :include, const_get("InstanceMethods") if const_defined?("InstanceMethods") base.class_eval(&@_included_block) if instance_variable_defined?("@_included_block") end end
included(base = nil, &block)
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Calls superclass method
# File lib/rails_core_extensions/active_support_concern.rb, line 126 def included(base = nil, &block) if base.nil? @_included_block = block else super end end