Void macro for Ruby

void.rb

module Void
  def void(method_name)
    method = instance_method(method_name)
    remove_method method_name

    define_method(method_name) do |*args, &block|
      method.bind(self).call(*args, &block).tap do |return_value|
        raise TypeError, 'unexpected return value' unless return_value.nil?
      end
    end

    method_name
  end
end

void_spec.rb

describe Void do
  subject {
    Class.new do
      extend Void

      void def is_void
        nil
      end

      void def is_not_void
        true
      end
    end.new
  }

  specify do
    expect(subject.is_void).to be_nil
  end

  specify do
    expect { subject.is_not_void }
      .to raise_error TypeError
  end
end

Done as an experiment in writing a private-style macro for Ruby 2.1 (this won't work in earlier versions of Ruby where def returns nil instead of the method name).