Decorator

Decorator

One-line pattern summary

A pattern that dynamically adds functionality at runtime through wrappers that surround an object.

Typical Unity use cases

• When applying weapon attributes in a composable way.
• When extending functionality without touching existing code.

Parts (roles)

• Component
• Decorator Base
• Concrete Decorator

Unity example (C#)

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

public interface IWeaponDamageCalculator
{
    int CalculateDamage();
}

public sealed class BaseWeaponDamageCalculator : IWeaponDamageCalculator
{
    public int CalculateDamage() => 10;
}

public abstract class WeaponDamageDecorator : IWeaponDamageCalculator
{
    protected readonly IWeaponDamageCalculator innerCalculator;

    protected WeaponDamageDecorator(IWeaponDamageCalculator innerCalculator)
    {
        this.innerCalculator = innerCalculator;
    }

    public abstract int CalculateDamage();
}

public sealed class FireDamageDecorator : WeaponDamageDecorator
{
    public FireDamageDecorator(IWeaponDamageCalculator innerCalculator) : base(innerCalculator) { }

    public override int CalculateDamage() => innerCalculator.CalculateDamage() + 5;
}

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 chain where functionality is added dynamically through wrappers.