class Module

def thread_mattr_reader(*syms, instance_reader: true, instance_accessor: true, default: nil) # :nodoc:

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

end
thread_mattr_reader :user, instance_reader: false
class Current

instance_reader: false or instance_accessor: false.
To omit the instance reader method, pass

# => NameError: invalid attribute name: 1_Badname
end
thread_mattr_reader :"1_Badname"
module Foo

The attribute name must be a valid method name in Ruby.

Thread.new { Current.user }.value # => nil
Current.user # => "DHH"
Current.user = "DHH"

end
thread_mattr_reader :user
module Current

The underlying per-thread class variable is set to +nil+, if it is not previously defined.
Defines a per-thread class attribute and creates class and instance reader methods. 
def thread_mattr_reader(*syms, instance_reader: true, instance_accessor: true, default: nil) # :nodoc:
  syms.each do |sym|
    raise NameError.new("invalid attribute name: #{sym}") unless /^[_A-Za-z]\w*$/.match?(sym)
    # The following generated method concatenates `name` because we want it
    # to work with inheritance via polymorphism.
    class_eval(<<-EOS, __FILE__, __LINE__ + 1)
      def self.#{sym}
        @__thread_mattr_#{sym} ||= "attr_\#{name}_#{sym}"
        ::ActiveSupport::IsolatedExecutionState[@__thread_mattr_#{sym}]
      end
    EOS
    if instance_reader && instance_accessor
      class_eval(<<-EOS, __FILE__, __LINE__ + 1)
        def #{sym}
          self.class.#{sym}
        end
      EOS
    end
    ::ActiveSupport::IsolatedExecutionState["attr_#{name}_#{sym}"] = default unless default.nil?
  end
end