diff options
Diffstat (limited to 'activesupport/lib/active_support/concern.rb')
| -rw-r--r-- | activesupport/lib/active_support/concern.rb | 148 |
1 files changed, 148 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/concern.rb b/activesupport/lib/active_support/concern.rb new file mode 100644 index 0000000000..5d356a0ab6 --- /dev/null +++ b/activesupport/lib/active_support/concern.rb @@ -0,0 +1,148 @@ +# frozen_string_literal: true + +module ActiveSupport + # A typical module looks like this: + # + # module M + # def self.included(base) + # base.extend ClassMethods + # base.class_eval do + # scope :disabled, -> { where(disabled: true) } + # end + # 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 + # + # class_methods do + # ... + # 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 + # def self.method_injected_by_foo + # ... + # end + # end + # end + # + # module Bar + # extend ActiveSupport::Concern + # include Foo + # + # included do + # self.method_injected_by_foo + # end + # end + # + # class Host + # include Bar # It works, now Bar takes care of its dependencies + # end + module Concern + class MultipleIncludedBlocks < StandardError #:nodoc: + def initialize + super "Cannot define multiple 'included' blocks for a Concern" + end + end + + def self.extended(base) #:nodoc: + base.instance_variable_set(:@_dependencies, []) + end + + def append_features(base) + if base.instance_variable_defined?(:@_dependencies) + base.instance_variable_get(:@_dependencies) << self + false + else + return false if base < self + @_dependencies.each { |dep| base.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? + if instance_variable_defined?(:@_included_block) + if @_included_block.source_location != block.source_location + raise MultipleIncludedBlocks + end + else + @_included_block = block + end + else + super + end + end + + def class_methods(&class_methods_module_definition) + mod = const_defined?(:ClassMethods, false) ? + const_get(:ClassMethods) : + const_set(:ClassMethods, Module.new) + + mod.module_eval(&class_methods_module_definition) + end + end +end |