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unity-coding

Implement gameplay and system code following Unity conventions

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SKILL.md

Unity Coding Skill

Write Unity C# code safely following best practices and conventions.

See also: Shared Conventions | Safety Guidelines

Purpose

Implement gameplay and system code changes that work in both Editor and headless/server contexts.

Code Style Rules

Namespaces

Always use namespaces matching folder structure:

csharp
// File: Assets/Scripts/Player/Movement/PlayerController.cs
namespace MyGame.Player.Movement
{
    public class PlayerController : MonoBehaviour
    {
    }
}

Assembly Definitions (asmdef)

  • Each major feature should have its own .asmdef
  • Reference other assemblies explicitly
  • Keeps compile times fast and dependencies clear
Assets/
  Scripts/
    Core/
      Core.asmdef           # Core utilities
    Player/
      Player.asmdef         # References: Core
    Networking/
      Networking.asmdef     # References: Core

Folder Layout

Assets/
  Scripts/
    Core/           # Utilities, extensions, base classes
    Player/         # Player-specific code
    Enemies/        # Enemy AI and behavior
    UI/             # UI controllers (not MonoBehaviours when possible)
    Networking/     # Netcode, server logic
    Data/           # ScriptableObjects, data containers
  Prefabs/
  Scenes/
  Resources/        # Use sparingly
  StreamingAssets/

Editor vs Runtime Code

No Editor-Time Side Effects

Code in Assets/Scripts/ should never:

  • Use #if UNITY_EDITOR for runtime logic
  • Access UnityEditor namespace in runtime code
  • Modify assets at runtime expecting Editor serialization

Editor-only code goes in:

Assets/
  Editor/
    MyEditorTools.cs    # UnityEditor namespace OK here

Headless-Friendly Code

For server/headless builds, avoid:

csharp
// BAD - crashes in headless
Camera.main.transform.position

// GOOD - null-safe
if (Camera.main != null)
    Camera.main.transform.position

Check for headless mode:

csharp
if (SystemInfo.graphicsDeviceType == GraphicsDeviceType.Null)
{
    // Running headless
}

ScriptableObjects vs MonoBehaviours

Use ScriptableObjects For:

  • Configuration data
  • Shared state between scenes
  • Event channels
  • Asset references
csharp
[CreateAssetMenu(fileName = "GameConfig", menuName = "Config/GameConfig")]
public class GameConfig : ScriptableObject
{
    public float playerSpeed = 5f;
    public int maxHealth = 100;
}

Use MonoBehaviours For:

  • Scene-specific behavior
  • Components that need Update/FixedUpdate
  • Physics interactions
  • Visual/audio feedback

Deterministic Server Code

For multiplayer/server authority:

csharp
// Use FixedUpdate for deterministic physics
void FixedUpdate()
{
    // Physics logic here
}

// Avoid Time.deltaTime in gameplay logic
// Use Time.fixedDeltaTime or fixed tick rates

// Avoid Random.Range for gameplay - use seeded random
private System.Random _seededRandom;

Allowed Tools

  • dotnet CLI (if using .NET tools)
  • git, gh
  • Text editors
  • No GUI assumptions

Patterns

Dependency Injection (Simple)

csharp
public class PlayerController : MonoBehaviour
{
    [SerializeField] private GameConfig _config;
    [SerializeField] private InputReader _inputReader;

    // Dependencies injected via Inspector
}

Event-Driven Architecture

csharp
// Event channel (ScriptableObject)
[CreateAssetMenu(menuName = "Events/Void Event")]
public class VoidEventChannel : ScriptableObject
{
    public event System.Action OnEventRaised;
    public void RaiseEvent() => OnEventRaised?.Invoke();
}

Policies

  • Follow existing project conventions first
  • Prefer composition over inheritance
  • Keep MonoBehaviours thin - delegate to plain C# classes
  • No magic strings - use constants or enums
  • Null-check external references (Camera.main, etc.)

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