Object-Oriented Programming in Ruby

Identifying Objects

In Ruby almost everything is an object - including numerics, booleans, strings and symbols - and each object in Ruby has a unique id.

1.object_id # => 3
"1".object_id # => 70102006679520
class Animal; end
Animal.object_id # => 70102006843460
Animal.new.object_id # => 70102007385240
Animal.new.object_id # => 70102024293860

Sending Messages

It could be argued that the basis of Ruby programming is sending messages to objects and dealing with their responses. 1+2 is really sending a message :+ to the object 1 with the argument of 2. The whole adding operation is really a syntactic sugar for 1.send(:+, 2)

Responding to Messages

Each object in Ruby responds to a message in one way or another. If the object knows how to handle the message it returns some value and if it does not it raises a NoMethodError.

class Animal
  def self.walk
    "Walking ..."

Animal.walk # => "Walking ..."
Animal.fly # => NoMethodError: undefined method `fly' for Animal:Class


As opposed to JavaScript where this might be undefined in Ruby there is always a self object. self means the current object within context of which methods are being defined and code evaluation is being effected. Even after directly accessing a Ruby console and without creating any objects there is a self.

$ irb
> self # => main

Methods defined within a context of main object are not anonymous functions as they are associated with the main object. This puts into question an existence in Ruby of pure procedural programming paradigm.

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