Replace Type Code with Class

Replace a primitive type code with a class.

“A class has a numeric type code that doesn’t affect its behavior.”

Enums on steroids.

graph LR
    A[Type = 1] -->|Refactoring| B[Type = BloodGroup.O]

When to apply (Smells)

• Primitive Obsession: Using int type = 1 for “O” blood.

Motivation

• Typos: type = 99 is valid for int but invalid for class.
• Location for logic: Ensure behaviors related to the type are in the type class.

Mechanics (Steps)

1. Create a class for the type code.
2. Replace the field with the new class.

Explanation

Problem

Class has a field type which is an int/string constants.

Solution

Create a new class BloodGroup and use instances of it.

Pros and Cons

Pros	Cons
Type safety	More boilerplate

Code example

Typescript

Before

After

PHP

Before

After