has_scope.rb

class UsersController < ApplicationController
  include User::SearchScope

  def index
    search_params = params[:user_search] || {}
    @users = apply_scopes(User, search_params)
  end
end

class User < ActiveRecord::Base
  # placed here only for convenience
  module SearchScope
    def self.included(base)
      base.has_scope :name
      base.has_scope :rating, default: 4 # setting default value
      base.has_scope :skills 
    end
  end

  scope :name, ->(name) { where('name like ?', "%#{name}%") }
  scope :rating, ->(rating) { where('rating > ?', rating) }
  # parsing values in the scope
  scope :skills, ->(skills) { tagged_with(skills.split(','), any: true) }
end