active_support_inflector => ActiveSupport::Inflector

constantize.rb

require 'active_support/inflector'

constantize = lambda { |str|
  result = ""

  str.split("_").inject("") { |acc, klass|
    begin
      try = acc + klass.classify

      try.constantize
      result = try
      try + "::"
    rescue NameError
      try
    end
  }

  result.constantize
}

constantize["active_support_inflector"]