Ruby Keyword Sugar

Problem

Imagine you have a public gem and it has a Point class defined as following

class Point
  def initialize(x, y)
    @x = x
    @y = y
  end

  def print
    "x: #{@x} and y: #{y}"
  end
end

Its easy to get an instance of Point class. You just pass positional argument - Point.new(5,7)

But lest say now you want to provide keyword arguments support. So you rewrite the initialize method.

def initialize(x:, y:)
  @x = x
  @y = y
end

You have just made a breaking change. All of the users of your gem who have been initializing Point with positional argument will now get error.

So how do you solve this problem? All we know is that both

Point.new(5,7) and Point.new(x: 5, y: 7) should work.

Solution

def initialize(_x=nil, _y=nil, x: _x, y: _y)
  x && y or raise ArgumentError, "Must supply x and y coordinates"
  @x = x
  @y = y
end