Extending The Built-In Ruby Classes.

A great ruby kata that demonstrates, and helps you understand how to extend the functionality of built-in ruby classes.

Problem Statement: Test your ability to extend built-in classes by adding the methods square(), sum(), average(), cube(), even(), and odd() to the Array class. These methods return a copy of the original array, after execution.

This is a great kata to learn and understand how classes, modules, and methods can be extended in Ruby.

Test Cases & Kata.

Ruby Kata: Extending The Built-In Ruby Classes.

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Here’s How I Solved It

class Array
  def square
     self.map{ |x| x**2 }
  end

  def cube
    self.map{ |x| x**3 }
  end

  def sum
    inject(0) { |result, el| result + el }
  end

  def average
   self.sum / self.size
  end

  def even
   self.select{ |x| x.to_i.even? }
  end

  def odd
   self.select{ |x| x.to_i.odd? }
  end
end

Precise / Elegant Solution(s)

This one’s by ant0 (and other people). ​

class Array
  def square
    map {|x| x*x}
  end

  def cube
    map {|x| x**3}
  end

  def average
    sum / size
  end

  def sum
    reduce(:+)
  end

  def even
    select(&:even?)
  end

  def odd
    select(&:odd?)
  end
end

Here’s another interesting solution by adamaig

class Array
  def square
    collect {|x| x * x }
  end

  def cube
    collect {|x| x * x * x }
  end

  def sum
    inject(0) {|x,y|  x + y }
  end

  def average
    sum / length 
  end

  def even
    select {|x| 0 == x % 2 }
  end

  def odd
    reject {|x| 0 == x % 2 }
  end
end

Extending Ruby Classes

Class, and module definitions in ruby are executable code. They’re parsed at compile time, and executed at runtime. Ruby is different than most other languages, in this regard. This makes it super easy to extend default functionality of classes, and modules. Read more here.

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