class Module

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

end
mattr_accessor :user, instance_accessor: false
class Current

Or pass instance_accessor: false, to opt out both instance methods.

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

end
thread_mattr_accessor :user, instance_writer: false, instance_reader: false
class Current

To opt out of the instance reader method, pass instance_reader: false.
To opt out of the instance writer method, pass instance_writer: false.

Account.user # => "DHH"
Customer.user # => "Rafael"
Customer.user = "Rafael"

end
class Customer < Account

is not changed.
Similarly, if the parent class changes the value, the value of subclasses
If a subclass changes the value, the parent class' value is not changed.

Account.new.user # => "DHH"
Account.user # => "DHH"
Account.user = "DHH"

end
thread_mattr_accessor :user
class Account

Defines both class and instance accessors for class attributes.

def thread_mattr_accessor(*syms, &blk)
  thread_mattr_reader(*syms, &blk)
  thread_mattr_writer(*syms, &blk)
end