143 lines
3.5 KiB
Ruby
143 lines
3.5 KiB
Ruby
module ActiveSupport
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# A typical module looks like this:
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#
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# module M
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# def self.included(base)
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# base.extend ClassMethods
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# base.class_eval do
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# scope :disabled, -> { where(disabled: true) }
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# end
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# end
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#
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# module ClassMethods
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# ...
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# end
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# end
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#
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# By using <tt>ActiveSupport::Concern</tt> the above module could instead be
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# written as:
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#
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# require 'active_support/concern'
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#
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# module M
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# extend ActiveSupport::Concern
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#
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# included do
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# scope :disabled, -> { where(disabled: true) }
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# end
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#
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# class_methods do
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# ...
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# end
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# end
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#
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# Moreover, it gracefully handles module dependencies. Given a +Foo+ module
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# and a +Bar+ module which depends on the former, we would typically write the
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# following:
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#
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# module Foo
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# def self.included(base)
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# base.class_eval do
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# def self.method_injected_by_foo
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# ...
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# end
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# end
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# end
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# end
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#
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# module Bar
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# def self.included(base)
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# base.method_injected_by_foo
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# end
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# end
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#
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# class Host
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# include Foo # We need to include this dependency for Bar
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# include Bar # Bar is the module that Host really needs
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# end
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#
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# But why should +Host+ care about +Bar+'s dependencies, namely +Foo+? We
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# could try to hide these from +Host+ directly including +Foo+ in +Bar+:
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#
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# module Bar
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# include Foo
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# def self.included(base)
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# base.method_injected_by_foo
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# end
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# end
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#
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# class Host
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# include Bar
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# end
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#
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# Unfortunately this won't work, since when +Foo+ is included, its <tt>base</tt>
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# is the +Bar+ module, not the +Host+ class. With <tt>ActiveSupport::Concern</tt>,
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# module dependencies are properly resolved:
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#
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# require 'active_support/concern'
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#
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# module Foo
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# extend ActiveSupport::Concern
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# included do
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# def self.method_injected_by_foo
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# ...
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# end
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# end
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# end
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#
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# module Bar
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# extend ActiveSupport::Concern
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# include Foo
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#
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# included do
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# self.method_injected_by_foo
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# end
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# end
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#
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# class Host
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# include Bar # works, Bar takes care now of its dependencies
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# end
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module Concern
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class MultipleIncludedBlocks < StandardError #:nodoc:
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def initialize
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super "Cannot define multiple 'included' blocks for a Concern"
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end
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end
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def self.extended(base) #:nodoc:
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base.instance_variable_set(:@_dependencies, [])
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end
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def append_features(base)
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if base.instance_variable_defined?(:@_dependencies)
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base.instance_variable_get(:@_dependencies) << self
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return false
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else
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return false if base < self
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@_dependencies.each { |dep| base.send(:include, dep) }
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super
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base.extend const_get(:ClassMethods) if const_defined?(:ClassMethods)
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base.class_eval(&@_included_block) if instance_variable_defined?(:@_included_block)
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end
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end
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def included(base = nil, &block)
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if base.nil?
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raise MultipleIncludedBlocks if instance_variable_defined?(:@_included_block)
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@_included_block = block
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else
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super
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end
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end
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def class_methods(&class_methods_module_definition)
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mod = const_defined?(:ClassMethods) ?
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const_get(:ClassMethods) :
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const_set(:ClassMethods, Module.new)
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mod.module_eval(&class_methods_module_definition)
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end
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end
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end
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