My name is Paul Ingles and I work at Forward where I work as a software developer on all kinds of interesting problems: high-volume low-latency distributed web services, 'big data' processing, data mining and analysis (as well as building the odd website). I'm lucky enough to work with Clojure, Ruby, Sinatra, Hadoop, Amazon EC2 and more every day (and the people aren't bad either).
Whilst working on a bit of code the other day we found this little nugget in the RDoc for Object#instance_variable_set:
Sets the instance variable names by symbol to object, thereby frustrating the efforts of the classâs author to attempt to provide proper encapsulation.
Brilliant!
The test:
def test_cannot_change_country_name_once_constructed country = Country.new(:name => 'UK') assert_raise RuntimeError do country.name = 'USA' endend
The class:
class Country < ActiveRecord::Base extend ImmutableModel immutable :name ...
The implementation:
module ImmutableModel def immutable(attr_name) define_method "#{attr_name}=" do |new_value| read_attribute(attr_name).nil? ? write_attribute(attr_name, new_value) : raise(RuntimeError, "You can't change #{attr_name} once it has been set") end endend
