unity-pattern-singleton

name: unity-pattern-singleton description: "Singleton" category: unity source: unity-design-patterns-skills source_path: patterns/singleton/SKILL.md

Singleton

Purpose

Guarantee that one meaningful instance exists and provide one controlled access path to it.

Use When

• Uniqueness is a real domain rule.
• A cross-scene service needs one lifetime owner.
• Bootstrap and teardown rules can be made explicit.

Avoid When

• Global access is only being used for convenience.
• Multiple instances may be valid later.

Unity Implementation Recipe

1. Document why uniqueness is required.
2. Handle duplicates and scene reloads explicitly.
3. Keep the API narrow.
4. Prefer composition over singleton if uniqueness is weak.

Common Pitfalls

• Hidden global dependencies.
• Duplicate instances during startup or play-mode reload.

Minimal Unity Sketch

public sealed class GameConfig : MonoBehaviour
{
    public static GameConfig Instance { get; private set; } = null!;

    private void Awake()
    {
        if (Instance != null && Instance != this) { Destroy(gameObject); return; }
        Instance = this;
        DontDestroyOnLoad(gameObject);
    }
}

Response Shape

• Say whether Singleton is actually the right fit.
• Map it to concrete Unity types, ownership, and lifecycle.
• Prefer a production-shaped skeleton over a long tutorial dump.
• Call out the simpler alternative if this pattern would be overengineering.