CODESAMPLE

Null Object - Ruby

Null Object Ruby

The Null Object pattern provides a substitute for an object that would otherwise be null or undefined. This avoids null checks throughout the code, simplifying logic and reducing the risk of NoMethodError exceptions. The null object implements the expected interface but has a default or “do nothing” behavior. In Ruby, this is naturally implemented using a class with methods that return sensible defaults (like an empty string or zero) instead of raising errors when called on a nil object. This example demonstrates a NullCustomer that responds to customer methods without requiring a real customer object to always exist.

# frozen_string_literal: true

# Define the Customer interface
class Customer
  def name
    raise NotImplementedError
  end

  def address
    raise NotImplementedError
  end

  def reward_points
    raise NotImplementedError
  end
end

# Concrete Customer implementation
class RealCustomer < Customer
  attr_reader :name, :address, :reward_points

  def initialize(name, address, reward_points)
    @name = name
    @address = address
    @reward_points = reward_points
  end
end

# Null Customer implementation
class NullCustomer < Customer
  def name
    ""
  end

  def address
    ""
  end

  def reward_points
    0
  end
end

# Example Usage
def print_customer_details(customer)
  puts "Name: #{customer.name}"
  puts "Address: #{customer.address}"
  puts "Reward Points: #{customer.reward_points}"
end

# Using a real customer
real_customer = RealCustomer.new("Alice", "123 Main St", 100)
print_customer_details(real_customer)

# Using a null customer
null_customer = NullCustomer.new
print_customer_details(null_customer)

def get_customer(id)
  # Simulate database lookup
  if id == 1
    RealCustomer.new("Bob", "456 Oak Ave", 50)
  else
    NullCustomer.new
  end
end

customer = get_customer(2)
print_customer_details(customer) # No need to check if customer is nil