Overriding class methods in Ruby

May 09 2006 rails | ruby | tips

Overriding class methods in Ruby

Class methods in Ruby are methods that work without being tied to any particular object (Java and PHP5 have static methods for similiar purpose). Class methods are distinguished from instance methods by placing the class name and a period in front of the method name. One thing that may not be obvious if you want to inherit class method is how to call equally named class method from parent class.

If you try to use super.class_method_name it would not work. That’s because class_method_name is class method and not instance method and as such it does not exists in object. Fortunately, classes in Ruby are objects too and you can interact with class like you interact with any other objects.

Enough talking, here is example:


class User
  def User.columns
    "name,email" 
  end
end

class Customer < User
  def Customer.columns
    self.superclass.columns + ",saldo" 
  end
end

puts Customer.columns # << name,email,saldo

comments feed

4 comments

# On May 16, 2006 at 14:05 PM, zimbatm said:
It could also be written like that : irb(main):001:0> class User irb(main):002:1> def self.columns irb(main):003:2> "name,email" irb(main):004:2> end irb(main):005:1> end => nil irb(main):006:0> class Customer < User irb(main):007:1> def self.columns irb(main):008:2> super + ",saldo" irb(main):009:2> end irb(main):010:1> end => nil irb(main):011:0> Customer.columns => "name,email,saldo"

# On May 16, 2006 at 14:05 PM, zimbatm said:

Woops, hope this one is better (what formatting do you use ?) :

irb(main):001:0> class User
irb(main):002:1>   def self.columns
irb(main):003:2>     "name,email"
irb(main):004:2>     end
irb(main):005:1>   end
=> nil
irb(main):006:0> class Customer < User
irb(main):007:1>   def self.columns
irb(main):008:2>     super + ",saldo"
irb(main):009:2>     end
irb(main):010:1>   end
=> nil
irb(main):011:0> Customer.columns
=> "name,email,saldo"

# On May 16, 2006 at 14:05 PM, zimbatm said:
damn : http://zimbatm.oree.ch/articles/2006/05/16/ruby-class-method-inheritance
# On May 17, 2006 at 01:05 AM, Bojan said:
That's even better zimbatm. Ops, I was tempted to write super.columns again :)