NoMethodError when using ruby refinements

Question

I'm using ruby's refinements to monkey-patch a method into the Math class like so:

module Radians
  refine Math do
    def radians(degrees)
      degrees * Math::PI / 180
    end
  end
end

I then try to call my monkey-patched method in a class like so:

class Foo
  using Radians
  def bar
    Math.radians(180)
  end
end

Foo.new.bar

This throws an undefined method `radians' for Math:Module (NoMethodError)

What am I doing wrong? My ruby version is 2.5.1p57. I've consulted the documentation and I think what I've done is correct, but obviously not.

Answer 1

You're defining an instance method, but calling a singleton method.

You need to refine the Math module's singleton class instead:

module Radians
  refine Math.singleton_class do
    def radians(degrees)
      degrees * Math::PI / 180
    end
  end
end