Flyweight

Flyweight

One-line pattern summary

A pattern that reduces memory usage for large numbers of objects by reusing shareable immutable state.

Typical Unity use cases

• When many instances share the same visual resources.
• When tile, icon, or projectile data contains lots of duplication.

Parts (roles)

• Flyweight
• Factory (Cache)
• Intrinsic / Extrinsic State

Unity example (C#)

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

using System.Collections.Generic;
using UnityEngine;

public sealed class ProjectileVisualFlyweight
{
    public readonly Sprite Sprite;

    public ProjectileVisualFlyweight(Sprite sprite)
    {
        Sprite = sprite;
    }
}

public sealed class ProjectileVisualFlyweightFactory
{
    private readonly Dictionary<string, ProjectileVisualFlyweight> cachedVisuals = new();

    public ProjectileVisualFlyweight Get(string visualKey, Sprite sprite)
    {
        if (!cachedVisuals.TryGetValue(visualKey, out ProjectileVisualFlyweight flyweight))
        {
            flyweight = new ProjectileVisualFlyweight(sprite);
            cachedVisuals.Add(visualKey, flyweight);
        }

        return flyweight;
    }
}

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 shareable intrinsic state is reused while extrinsic state is injected from context.