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module ActiveSupport
# A typical module looks like this:
#
# module M
# def self.included(base)
# base.extend ClassMethods
# scope :disabled, where(:disabled => true)
# end
#
# module ClassMethods
# ...
# end
# end
#
# By using <tt>ActiveSupport::Concern</tt> 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
# 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 <tt>base</tt> is the +Bar+ module,
# not the +Host+ class. With <tt>ActiveSupport::Concern</tt>, 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
#
module Concern
def self.extended(base)
base.instance_variable_set("@_dependencies", [])
end
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.class_eval(&@_included_block) if instance_variable_defined?("@_included_block")
end
end
def included(base = nil, &block)
if base.nil?
@_included_block = block
else
super
end
end
end
end
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