Change Value to Reference

Turn a value object into a reference object.

“You have a class with many equal instances that you want to replace with a single object.”

Singleton-ish behavior for entities.

graph LR
    A[Many 'Customer' Copies] -->|Refactoring| B[Shared 'Customer']

When to apply (Smells)

  • Data inconsistency: Updating one copy doesn’t update others.

Motivation

  • Ensure that changes to one conceptual object (like a Customer) are reflected everywhere.

Mechanics (Steps)

  1. Replace the constructor with a Factory Method.
  2. Make the factory method return existing instances if available (Repository pattern).

Explanation

Problem

You create a new object for the same entity every time (e.g., new Customer(“John”)). If you change John’s address in one order, it doesn’t update in another order.

Solution

Convert the object to a reference object so all orders point to the same Customer instance.

Pros and Cons

Pros Cons
  • Consistency
    		•
  • Memory management (harder to GC)
    		•

    Comparison

    • Inverse Refactoring: Change Reference to Value.

    Code example

    Typescript

    Before

    After

    PHP

    Before

    After