Hacky and dirty way to implement type hinting in ruby classes

hinting-module.rb

# Author: Maxime Buffa <mbuffa@gmail.com>
# Copied from: https://github.com/mbuffa/ultima
# This module allow some sort of type hinting for instance methods.
# Set required variable types with #hint, and don't forget to call
# #hint_method(your_method_symbol) after its definition.
# It'll raise an ArgumentError if types mismatch.
module Hinting
  @@hinting = Hash.new()

  def self.extended(base)
    base.class_eval do
      define_singleton_method(:hint_method) do |method_symbol|
        meth = instance_method(method_symbol)

        define_method(method_symbol) do |*args, &block|
          meth.parameters.map(&:last)
                         .each.with_index do |param_sym, i|
            args.each.with_index do |arg, j|
              # TODO: Find a better way than this...
              next if i != j

              type_hint = @@hinting[param_sym]

              if !type_hint.nil? && type_hint != arg.class
                raise ArgumentError, "#{param_sym} must be #{type_hint}"
              end
            end
          end
          meth.bind(self).call(*args, &block)
        end
      end
    end
  end

  def hint(symbols, type)
    Array(symbols).each do |param_sym|
      @@hinting[param_sym] = type
    end
  end

  def hinting
    @@hinting
  end
end

some-class.rb

YourClass
  extend Hinting

  hint :a, String
  hint :b, Fixnum

  def initialize(a, b)
    @a = a
    @b = b
  end
  hint_method :initialize
end