Focus on Messages

In this chapter, you will learn how to write message centric Ruby programs.

Avoid Over Emphasis on Objects

Alan Kay coined the term Object Oriented Programming. He has expressed regret that he overemphasized the benefits of objects.

I'm sorry that I long ago coined the term "objects" for this topic because it gets many people to focus on the lesser idea. The big idea is "messaging". The Japanese have a small word - ma - for "that which is in between" - perhaps the nearest English equivalent is "interstitial".

The key in making great and grow-able systems is much more to design how its modules communicate rather than what their internal properties and behaviors should be.

                              -- Alan Kay


Sending a Message

In Smalltalk, you can send factorial message to a number object. In Ruby, when you do the same:


You will get an error:

NoMethodError: undefined method ‘factorial’ for 3:Fixnum

Open Fixnum Class

Ruby is flexible, it has open classes. We can open the Fixnum class and define factorial method.

class Fixnum
  def factorial
    (1..self).reduce(1, :*)

We can now send factorial method to the Fixnum object.

p 3.factorial

This prints:


The above solution looks much more elegant than doing:


Using Refinements

It is debatable whether opening a Fixnum class to define factorial is a good idea. It is better to use refinements instead to avoid global impact in your programs.

module MyModule
  refine Fixnum do
    def factorial
      (1..self).reduce(1, :*)

using MyModule

p 3.factorial

This prints the same value 6. There is a drawback to this approach. We need to know the name of the module in the using declaration before we can call the factorial method. This creates a dependency. It's a trade-off you need to make between reducing the impact vs knowing the name of a module.


In this chapter, you learned how you can make your Ruby programs more message centric. We can use open classes and refinements for this purpose. The real power is in the messaging.

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