Module to get decorators for POROs to make `attr_*` private

private_attr_methods_decorators.rb

module PrivateAttrMethodsDecorators
  module Explicit
    module ClassMethods
      def private_attr_reader(*attributes)
        attributes.each do |attr|
          attr_reader attr

          private attr
        end
      end

      def private_attr_writer(*attributes)
        attributes.each do |attr|
          attr_writer attr
          attr_writer_method = "#{attr}="

          private attr_writer_method
        end
      end

      def private_attr_accessor(*attributes)
        attributes.each do |attr|
          attr_accessor attr
          attr_writer_method = "#{attr}="

          private attr, attr_writer_method
        end
      end
    end

    def self.included(base)
      base.extend(ClassMethods)
    end
  end

  module Implicit
    module ClassMethods
      def private_attr(mode, *attributes)
        attributes.each do |attr|
          send("attr_#{mode}", attr)

          case mode
          when :reader
            private attr
          when :writer
            attr_writer_method = "#{attr}="
            private attr_writer_method
          when :accessor
            attr_writer_method = "#{attr}="
            private attr, attr_writer_method
          end
        end
      end
    end

    def self.included(base)
      base.extend(ClassMethods)
    end
  end
end

class Service
  include PrivateAttrMethodsDecorators::Explicit
  private_attr_reader   :foo, :bar
  private_attr_writer   :baz
  private_attr_accessor :alakazam

  def initialize(foo)
    @foo = foo
  end

  def call
    puts foo

    self.baz = "baz"
    p self

    self.alakazam = "alakazam"
    puts alakazam
  end
end

service = Service.new("foo")
service.call
# OUTPUT
# foo
# #<Service:0x007fb4934ff458 @foo="foo" @baz="baz">
# alakazam

service.foo                     # => Undefined method
service.baz                     # => Undefined method
service.alakazam                # => Undefined method

service.foo = "fou"             # => Undefined method
service.baz = "boz"             # => Undefined method
service.alakazam = "olokozom"   # => Undefined method