module ActiveSupport::Configurable::ClassMethods

# File activesupport/lib/active_support/configurable.rb, line 107
def config_accessor(*names, instance_reader: true, instance_writer: true, instance_accessor: true) # :doc:
  names.each do |name|
    raise NameError.new("invalid config attribute name") unless /\A[_A-Za-z]\w*\z/.match?(name)

    reader, reader_line = "def #{name}; config.#{name}; end", __LINE__
    writer, writer_line = "def #{name}=(value); config.#{name} = value; end", __LINE__

    singleton_class.class_eval reader, __FILE__, reader_line
    singleton_class.class_eval writer, __FILE__, writer_line

    if instance_accessor
      class_eval reader, __FILE__, reader_line if instance_reader
      class_eval writer, __FILE__, writer_line if instance_writer
    end
    send("#{name}=", yield) if block_given?
  end
end

Allows you to add shortcut so that you don't have to refer to attribute through config. Also look at the example for config to contrast.

Defines both class and instance config accessors.

class User
  include ActiveSupport::Configurable
  config_accessor :allowed_access
end

User.allowed_access # => nil
User.allowed_access = false
User.allowed_access # => false

user = User.new
user.allowed_access # => false
user.allowed_access = true
user.allowed_access # => true

User.allowed_access # => false

The attribute name must be a valid method name in Ruby.

class User
  include ActiveSupport::Configurable
  config_accessor :"1_Badname"
end
# => NameError: invalid config attribute name

To omit the instance writer method, pass instance_writer: false. To omit the instance reader method, pass instance_reader: false.

class User
  include ActiveSupport::Configurable
  config_accessor :allowed_access, instance_reader: false, instance_writer: false
end

User.allowed_access = false
User.allowed_access # => false

User.new.allowed_access = true # => NoMethodError
User.new.allowed_access        # => NoMethodError

Or pass instance_accessor: false, to omit both instance methods.

class User
  include ActiveSupport::Configurable
  config_accessor :allowed_access, instance_accessor: false
end

User.allowed_access = false
User.allowed_access # => false

User.new.allowed_access = true # => NoMethodError
User.new.allowed_access        # => NoMethodError

Also you can pass a block to set up the attribute with a default value.

class User
  include ActiveSupport::Configurable
  config_accessor :hair_colors do
    [:brown, :black, :blonde, :red]
  end
end

User.hair_colors # => [:brown, :black, :blonde, :red]