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tag: v2.3.11
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require 'active_support/core_ext/kernel/singleton_class'
require 'active_support/core_ext/module/remove_method'
class Class
# Declare a class-level attribute whose value is inheritable and
# overwritable by subclasses:
#
# class Base
# class_attribute :setting
# end
#
# class Subclass < Base
# end
#
# Base.setting = true
# Subclass.setting # => true
# Subclass.setting = false
# Subclass.setting # => false
# Base.setting # => true
#
# This matches normal Ruby method inheritance: think of writing an attribute
# on a subclass as overriding the reader method.
#
# For convenience, a query method is defined as well:
#
# Subclass.setting? # => false
#
# Instances may overwrite the class value in the same way:
#
# Base.setting = true
# object = Base.new
# object.setting # => true
# object.setting = false
# object.setting # => false
# Base.setting # => true
#
# To opt out of the instance writer method, pass :instance_writer => false.
#
# object.setting = false # => NoMethodError
def class_attribute(*attrs)
instance_writer = !attrs.last.is_a?(Hash) || attrs.pop[:instance_writer]
attrs.each do |name|
class_eval <<-RUBY, __FILE__, __LINE__ + 1
def self.#{name}() nil end
def self.#{name}?() !!#{name} end
def self.#{name}=(val)
singleton_class.class_eval do
remove_possible_method(:#{name})
define_method(:#{name}) { val }
end
end
def #{name}
defined?(@#{name}) ? @#{name} : singleton_class.#{name}
end
def #{name}?
!!#{name}
end
RUBY
attr_writer name if instance_writer
end
end
end
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