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Jess Lee
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Explain the 'super' keyword in ruby like I'm five

#explainlikeimfive #ruby #rails

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edizle585 profile image
Elijah Logan •

So lets say your mom makes super smacking pb &j's using her super smacking pb & j technique (all she does is remove the crust). But today mom had to hurry to work so brother B is making breakfast. Your not sure if b can make pb & j's like mom but he assures you that he's used ( super ) to get moms skill passed down to him so he's qualified. Using super B made you some super smacking pb & j's

class Mom-PB-Technique
def corner-cut(bread)
for corner in bread
corner.cut crust
return bread
end

class B-PB-Technique < Mom-PB-Technique
def corner-cut
super
end

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cathodion profile image
Dustin King • • Edited

Doesn't doing B-PB-Technique < Mom-PB-Tecnhnique already give you all of mom's methods?

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zspencer profile image
Zee •

Yes, it does. super is most useful when over-riding the behavior from a method provided in the ancestor chain. I would revise the example to the following:

class MomPBTechnique def corner_cut(bread) for corner in bread corner.cut crust end return bread end class MyPBTechnique < MomPBTechnique # I like *one* corner to not be cut! def corner_cut first_corner = self.bread[0] # Gets the first corner self.bread = bread.slice(1, -1) # Sets the bread to only the last 3 corners super # Calls the `corner_cut` method defined in `MomPBTechnique` return bread.unshift(first_corner) # Places the un-cut first corner back in the bread end end

This more clearly demonstrates how super can be used to re-use-but-still-change behavior in the class hierarchy.

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johand profile image
Johan • • Edited

With super you can call a method on the parent class with the same name in the child class, for example:

class Foo def my_method 'Hello there' end end class Bar < Foo def my_method super end end b = Bar.new b.my_method # => Hello there
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Ruby search a method #my_method in the ancestor chain, if the method not exist it will show an error NoMethodError

`my_method': super: no superclass method `my_method' for #<Bar:0x0000564740b32170> (NoMethodError)
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cathodion profile image
Dustin King • • Edited

When you inherit from a parent class, sometimes you want the child's method to behave slightly differently but still use the parent method's behavior.

Let's say you have a Greeter, and their job is to say hi to everyone they meet. If they have the person's name, they'll greet them by name.

class Greeter def greet(name=nil) if name puts "Hi, #{name}, nice to meet you!" else puts "Hi, nice to meet you!" end end end Greeter.new.greet #=> Hi, nice to meet you! Greeter.new.greet 'Jess' #=> Hi, Jess, nice to meet you!
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Now suppose we hire a new greeter from the planet Marklar, who has a religious belief that everyone's name is Marklar. When their greet method calls super, it calls the greet method from their parent class, Greeter:

class MarklarGreeter < Greeter def greet super 'Marklar' end end MarklarGreeter.new.greet #=> Hi, Marklar, nice to meet you MarklarGreeter.new.greet 'Jess' #=> ArgumentError: wrong number of arguments (given 1, expected 0)
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Okay, we still need greet to take a name parameter, so that we can use a MarklarGreeter anywhere we use a Greeter. This is called the Liskov Substitution Principle. I can't find a link that explains that like you're five, but it basically says an instance of a child class should be usable anywhere you can use an instance of the parent class.

class MarklarGreeter < Greeter def greet(name=nil) # We accept a name parameter here, but we ignore it # because everyone's name is Marklar super 'Marklar' end end MarklarGreeter.new.greet #=> Hi, Marklar, nice to meet you! MarklarGreeter.new.greet 'Jess' #=> Hi, Marklar, nice to meet you!
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More info about Ruby's super here.

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chenge profile image
chenge •

IMHO, super is alias of father or mother.

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imrawal profile image
Mee Lana • • Edited

Is it good or bad to chain method in super like in below activerecord(5.1.6) code,

# 'delivery_timings' is a db field attribute class Country < ApplicationRecord # expects array of times and converts to string ie. ['08:00-12:00', '14:00-16:00'] to "08:00-12:00,14:00-16:00" def delivery_timings=(val) return super(val) if val.blank? super(val.reject(&:blank?).join(',')) end # converts string value to array of times ie. "08:00-12:00,14:00-16:00" to ['08:00-12:00', '14:00-16:00'] def delivery_timings return super if super.blank? super.split(',') end end

Although the code works, I'm smelling on code(may be wrong).

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martin profile image
Martin Beentjes •

super is your parent.