Super, or Super()?

TLDR

• super equals super(*args), which brings ALL args to the inherited method
• super()..., is just super() that simply invokes the inherited method

Keyword "Super" in Ruby

When super is used in a method, e.g., Dog#eat, super calls the method of the same name in parent class, i.e., #eat in Animal:

class Animal
  def eat
   puts "eating"
  end
end
 
class Dog < Animal
  def eat
    # calls super here
    super
  end
end
 
doggy = Dog.new
p doggy.eat # "eating"

Wait, ArgumentError?

Things start to get messy when we decide to explicitly pass arguments to super:

class Animal
  def eat(food)
    puts "eating #{food}"
  end
end
 
class Dog < Animal
  def eat(food1, food2)
    # super without declaring args
    super
    puts "eating #{food2} as well"
  end
end
 
class Cat < Animal
  def eat(food1, food2)
    # super with args
    super(food1)
    puts "eating #{food2} as well"
  end
end
 
doggy = Dog.new
kitty = Cat.new
doggy.eat("bento", "sushi") # "ArgumentError: (given 2, expected 1)"
kitty.eat("bento", "sushi") # "eating bento" & "eating sushi as well"

Super vs. Super()

• super equals super(*args), which brings ALL args to the inherited method
• Use super() when you just want to call the method inherited from Parent without passing args

Examples

Say, we have a class, called Animal:

class Animal
  def eat
    puts "eating"
  end
end

Scenarios

• Use super in #eat:

  class Dog < Animal
    def eat(food1, food2)
      super
      puts "eating #{food2} as well"
    end
  end
   
  doggy = Dog.new
  doggy.eat("bento", "sushi") # "ArgumentError: (given 2, expected 0)"
  #                                              ^^^^^^^

• Use super(arg) in #eat:

  class Cat < Animal
    def eat(food1, food2)
      # super(arg)
      super(food1)
      puts "eating #{food2} as well"
    end
  end
   
  kitty = Cat.new
  kitty.eat("bento", "sushi") # "ArgumentError: (given 1, expected 0)"
  #                                              ^^^^^^^

• Use super() in #eat:

  class Bird < Animal
    def eat(food1, food2)
      # Just super()
      super()
      puts "eating #{food1} and #{food2} as well"
    end
  end
   
  birdy = Bird.new
  birdy.eat("bento", "sushi") # program executes; prints
  # eating
  # eating bento and sushi as well

References

• Object#super by ruby-doc.org

• How to Use The Ruby Super Keyword by Jesus Castello

• super vs super() in Ruby by Carson Tang