class Module

def thread_mattr_writer(*syms) # :nodoc:

:nodoc:
Current.new.user = "DHH" # => NoMethodError

end
thread_mattr_writer :user, instance_writer: false
class Current

instance_writer: false or instance_accessor: false.
If you want to opt out the instance writer method, pass

Thread.current[:attr_Current_user] # => "DHH"
Current.user = "DHH"

end
thread_mattr_writer :user
module Current

allow assignment to the attribute.
Defines a per-thread class attribute and creates a class and instance writer methods to 
def thread_mattr_writer(*syms) # :nodoc:
  options = syms.extract_options!
  syms.each do |sym|
    raise NameError.new("invalid attribute name: #{sym}") unless sym =~ /^[_A-Za-z]\w*$/
    class_eval(<<-EOS, __FILE__, __LINE__ + 1)
      def self.#{sym}=(obj)
        Thread.current["attr_"+ name + "_#{sym}"] = obj
      end
    EOS
    unless options[:instance_writer] == false || options[:instance_accessor] == false
      class_eval(<<-EOS, __FILE__, __LINE__ + 1)
        def #{sym}=(obj)
          Thread.current["attr_"+ self.class.name + "_#{sym}"] = obj
        end
      EOS
    end
  end
end