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How to Use The Ruby Super Keyword

What does the super keyword do in Ruby?

It calls a method on the parent class with the same name as the method that calls super.

For example:

If you call a method named i_like_chocolate, and then you call super within that method, Ruby will try to find another method with that same name on the parent class of whoever owns this method.

This keeps bubbling up through the class ancestry chain like a regular method call.

If the method doesn’t exist it will trigger a NoMethodError exception, and if a method_missing is found it will use that.

Now:

Let’s take a look @ some code examples!

Super Without Arguments

In the following example we have a Cat class that inherits from Animal.

The Cat class has a name method that uses super to call the same method on its parent class (Animal).

Here’s the code:

class Animal
  def name
    puts "Animal"
  end
end

class Cat < Animal
  def name
    super
  end
end

cat = Cat.new
cat.name

# "Animal"

The Ruby super keyword behaves differently when used with or without arguments.

Without arguments:

It will pass along the arguments used for the original method call to the new one, including keyword arguments & a block if given.

Here's an example:

def puts(*)
  super
end

puts 1, 2, 3

This method, defined outside of any class, will belong to Object. This means it will be called before the original puts method.

Now:

When you call puts you're calling this new method we have created which then uses super to call the original puts.

When to Use Super vs Super()

We just looked at how to use super for calling parent methods.

But what if the parent method doesn't take the same number of arguments?

In that case you can use:

  • super() for no arguments
  • super(arg1, arg2, ...) to choose what arguments you want to pass

Example:

def puts
  super()
end

Notice how the parenthesis have special meaning here, unlike a regular method call.

A few more things to know about super:

  • It can only be used inside a method
  • It returns the result from calling the parent method
  • It can be called multiple times

The bolded line (super returns results) is key to understanding some of the uses for super that you may find in the wild.

You can use super to implement the decorator pattern, or if you call it inside the initialize method it can be used to initialize instance variables on the parent class.

Summary

You've learned about the Ruby super keyword, what it is & how it works in different situations!

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