Super keyword in Ruby

Question

What is the super for in this code?

def initialize options = {}, &block   @filter = options.delete(:filter) || 1   super end 

As far as I know it's like calling the function recursively, right?

Answer 1

no... super calls the method of the parent class, if it exists. Also, as @EnabrenTane pointed out, it passes all the arguments to the parent class method as well.

Answer 2

super calls a parent method of the same name, with the same arguments. It's very useful to use for inherited classes.

Here's an example:

class Foo   def baz(str)     p 'parent with ' + str   end end  class Bar < Foo   def baz(str)     super     p 'child with ' + str   end end  Bar.new.baz('test') # => 'parent with test' \ 'child with test' 

There's no limit to how many times you can call super, so it's possible to use it with multiple inherited classes, like this:

class Foo   def gazonk(str)     p 'parent with ' + str   end end  class Bar < Foo   def gazonk(str)     super     p 'child with ' + str   end end  class Baz < Bar   def gazonk(str)     super     p 'grandchild with ' + str   end end  Baz.new.gazonk('test') # => 'parent with test' \ 'child with test' \ 'grandchild with test' 

If there's no parent method of the same name, however, Ruby raises an exception:

class Foo; end  class Bar < Foo   def baz(str)     super     p 'child with ' + str   end end  Bar.new.baz('test') # => NoMethodError: super: no superclass method ‘baz’