RebootKit/Runtime/Engine/Code/Extensions/GameObjectEx.cs

using UnityEngine;

namespace RebootKit.Engine.Extensions {
    public static class GameObjectEx {
        public static T GetOrAdd<T>(this GameObject gameObject) where T : Component {
            T component = gameObject.GetComponent<T>();

            if (component == null) {
                component = gameObject.AddComponent<T>();
            }

            return component;
        }

        public static void DestroyChildren(this GameObject gameObject) {
            gameObject.transform.DestroyChildren();
        }

        public static T OrNull<T>(this T instance) where T : Object {
            return instance ? instance : null;
        }

        public static void SetLayersRecursively(this GameObject gameObject, int layer) {
            gameObject.layer = layer;
            gameObject.transform.ForEachChild(child => {
                child.gameObject.SetLayersRecursively(layer);
            });
        }
    }
}