Ruby operator-overloading not working properly for a custom class object

Question

I need some help with my +/- overridden method, it is not affecting the elements of wektor array.

class Wektor
  attr_accessor :coords

  def initialize(length)
    @coords = Array.new(length, 0)
  end

  def set!(w)
    @coords = w.dup

    self
  end

  %i(* /).each do |op|
    define_method(op) do |n|
      coords.map! { |i| i.send(op, n) }

      self
    end
  end

  %i(- +).each do |op|
    define_method(op) do |v|
      @coords.zip(v).map { |a, b| a.send(op, b) }

      self
    end
  end

  def shift_right!
    coords.rotate!
    coords[0] = 0

    self
  end


end

So basically if a = Wektor.new(4).set!([1,2,3,4] and b = Wektor.new(4).set!([1,1,1,1] I want a-b to set a = [0,1,2,3] What is wrong with this method? It is not changing anything - a is still set to [1,2,3,4].

I tried debugging with IRB but it doesn't give me any clue on what is wrong.

The code looks good to me, but I'm a beginner when it comes to writing ruby-way code (I'm not the author of this piece of code) and I have trouble spotting the error.

* and / is working OK, the vector is supposed to be multiplied/divided by scalar.

Nick Veys · Accepted Answer · 2015-01-07 19:14:55Z

1

Try this instead:

%i(- +).each do |op|
  define_method(op) do |v|
    @coords = @coords.zip(v.coords).map { |a, b| a.send(op, b) }
    self
  end
end

You want to zip the array, so calling coords on v makes that work. Also, map performs the given block and returns the collected results, you were discarding them.

Are you aware that Ruby has a Vector class?

2.1.5 :001 > require 'matrix'
 => true 
2.1.5 :002 > a = Vector[1,2,3,4]
 => Vector[1, 2, 3, 4] 
2.1.5 :003 > b = Vector[1,1,1,1]
 => Vector[1, 1, 1, 1] 
2.1.5 :004 > a - b
 => Vector[0, 1, 2, 3] 
2.1.5 :005 > a * 3
 => Vector[3, 6, 9, 12]

answered Jan 7, 2015 at 19:14

Nick Veys

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4 Comments

Asunez Over a year ago

Yes, I'm aware. However I need to keep this as simple as possible, hence the custom class. Your code works as intended, thank you very much!

Nick Veys Over a year ago

Glad I could help, though I'm confused how defining your own classes keeps things simple!

Asunez Over a year ago

one small question - I can't find a substitute for my shift_right! method in the default Ruby Vector class. What is the proper way to do this? vec.to_a, then shift/pop on an array and finally copy the modified array to my Vector?

Nick Veys Over a year ago

Probably the easiest way, yeah. You add that method to the built in Vector class too.

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