Ruby class variables

Question

The ruby class-instance stuff is giving me a headache. I understand given this...

class Foo   @var = 'bar' end 

...that @var is a variable on the created class's instance.

But how do I create a sub-class overridable class variable?

Here is an example of what I would do in Python:

class Fish: var = 'fish' def v(self):     return self.var  class Trout(Fish):     var = 'trout'  class Salmon(Fish):     var = 'salmon'  print Trout().v() print Salmon().v() 

Which outputs:

trout salmon 

How do I do the same thing in ruby?

Answer 1

To contrast @khelll's answer, this uses instance variables on the Class objects:

class Fish   # an instance variable of this Class object   @var = 'fish'    # the "getter"   def self.v     @var   end    # the "setter"   def self.v=(a_fish)     @var = a_fish   end end  class Trout < Fish   self.v = 'trout' end  class Salmon < Fish   self.v = 'salmon' end  p Trout.v   # => "trout" p Salmon.v  # => "salmon" 

Edit: to give instances read-access to the class's instance variable:

class Fish   def type_of_fish     self.class.v   end end  p Trout.new.type_of_fish   # => "trout" p Salmon.new.type_of_fish  # => "salmon" 

Answer 2

@var mentioned above is called class instance variable, which is different from instance variables... read the answer here to see the diff.

Anyway this is the equivalent Ruby code:

class Fish   def initialize     @var = 'fish'   end    def v     @var   end end  class Trout < Fish   def initialize     @var = 'trout'    end end  class Salmon < Fish   def initialize     @var = 'salmon'    end end  puts Trout.new.v puts Salmon.new.v