unity-composition

name	unity-composition
description	Unity Composition Patterns

Unity Composition Patterns

Use this skill when structuring Unity code with component architecture, interface-based design, dependency injection, or cross-object communication patterns.

When to Use Inheritance

Inheritance is not forbidden -- it is useful for:

// Base class for common MonoBehaviour boilerplate
public abstract class Singleton<T> : MonoBehaviour where T : MonoBehaviour
{
    public static T Instance { get; private set; }

    protected virtual void Awake()
    {
        if (Instance != null)
        {
            Destroy(gameObject);
            return;
        }
        Instance = (T)(MonoBehaviour)this;
        DontDestroyOnLoad(gameObject);
    }
}

// Clean singleton declaration
public class AudioManager : Singleton<AudioManager>
{
    protected override void Awake()
    {
        base.Awake();
        // AudioManager-specific init
    }
}

// Abstract base for similar UI screens
public abstract class MenuScreen : MonoBehaviour
{
    [SerializeField] private CanvasGroup _canvasGroup;

    public virtual void Show()
    {
        gameObject.SetActive(true);
        _canvasGroup.alpha = 1f;
        _canvasGroup.interactable = true;
        _canvasGroup.blocksRaycasts = true;
    }

    public virtual void Hide()
    {
        _canvasGroup.interactable = false;
        _canvasGroup.blocksRaycasts = false;
        gameObject.SetActive(false);
    }
}

public class MainMenuScreen : MenuScreen
{
    public override void Show()
    {
        base.Show();
        // Refresh leaderboard, etc.
    }
}

Rule of thumb: Use inheritance for framework-level base classes (singletons, UI screens, state bases). Use composition for gameplay entities (enemies, weapons, interactables).

Architecture Decision Guide

Situation	Pattern
Components on same GameObject	Direct reference via GetComponent (cached)
Parent-child components	GetComponentInChildren / GetComponentInParent
Same entity, loose coupling	C# events (subscribe in OnEnable, unsubscribe in OnDisable)
Cross-entity, same scene	ScriptableObject event channels or direct reference
Cross-scene	ScriptableObject event channels or Service Locator
Global services (audio, input)	Singleton or Service Locator
Large project, testability	DI framework (VContainer)
Spawned objects need references	Init method injection
Entity variants (easy/hard enemy)	Prefab variants
Entity types (enemy/turret/trap)	Component composition on prefabs

Topic Pages

• Composition Over Inheritance