Composition over inheritance

Basically, while writing ruby codes, I avoid using inheritance because inheritance sometimes produce unnecessary tight couplings.

Example

class Vehicle   
  def start_engine
  end    
  def stop_engine  
  end 
end  

class Car < Vehicle   
  def drive     
    start_engine 
    stop_engine  
  end 
end

In this case, Car class knows about the codes of Vehicle class. If we create objects that don’t use an engine, it will necessary to take much time to change the codes.

Solution

We should use compositions. In other words, we should define Engine object.

class Car   
  def initialize     
    @engine = Engine.new   
  end    
  def drive     
    @engine.start
    @engine.stop   
  end 
end  
class Engine   
  def start 
  end    
  def stop    
  end 
end

In this case, Engine class was separated from Car class. Moreover, it has become easy to make new objects that don’t use an engine.

My LinkedIn account is below! Please contact me!

https://www.linkedin.com/in/tomoharu-tsutsumi-56051a126/