Factory Method

One-line pattern summary

A pattern that delegates the actual creation responsibility of a factory method to subclasses.

Typical Unity use cases

• When projectile creation rules differ by weapon type.
• When type-specific initialization logic should be separated.

Parts (roles)

• Creator
• Concrete Creator
• Product

Unity example (C#)

The code below is a simplified Unity example based on the scenario described above.

using UnityEngine;

public interface IProjectile
{
    void Fire(Vector3 startPosition, Vector3 direction);
}

public abstract class ProjectileSpawner : MonoBehaviour
{
    public void Shoot(Vector3 startPosition, Vector3 direction)
    {
        IProjectile projectile = CreateProjectile();
        projectile.Fire(startPosition, direction);
    }

    protected abstract IProjectile CreateProjectile();
}

Advantages

• It clarifies module boundaries and reduces coupling.
• Features can be extended or integrated without modifying existing code.

Things to watch out for

• If wrapper layers become too deep, debugging gets harder.
• Interfaces should stay small so responsibility boundaries do not blur.

Interaction diagram

This shows the flow where the parent keeps the creation procedure while subclasses choose the actual type.

flowchart LR

  client["Client"]
  creator["Creator.Spawn()"]
  factory_method["CreateProduct()"]
  concrete_a["BulletSpawner"]
  concrete_b["EffectSpawner"]
  product["IProduct"]

  client --> creator
  creator --> factory_method
  factory_method -->|mode A| concrete_a
  factory_method -->|mode B| concrete_b
  concrete_a --> product
  concrete_b --> product
  product --> client