patching_named_scope_arity.rb

module NamedScopeArity
  extend ActiveSupport::Concern
  module ClassMethods
    def scope(name, scope_options = {})
      super
      redefined = false
      eigenclass = instance_eval do
        class << self
          self
        end
      end
      if scope_options.class == Proc
        redefined = true
        case scope_options.arity
        when 0
          eigenclass.instance_eval do
            define_method "#{name}_with_arity_0".to_sym do
              send("#{name}_without_arity_0".to_sym)
            end
            alias_method_chain name, :arity_0
          end
          redefined = true
        when 1
          eigenclass.instance_eval do
            define_method "#{name}_with_arity_1".to_sym do |arg1|
              send("#{name}_without_arity_1".to_sym, arg1)
            end
            alias_method_chain name, :arity_1
          end
        else
          redefined = false
        end
      end
      if !redefined
        eigenclass.instance_eval do
          define_method("#{name}_with_any_arity".to_sym) do |*args|
            send("#{name}_without_any_arity".to_sym, *args)
          end
          alias_method_chain name, :any_arity
        end
      end
    end
  end
end

ActiveRecord::Base.send(:include, NamedScopeArity)