Singleton

using UnityEngine;

public class Singleton<T> : MonoBehaviour where T : MonoBehaviour
{
    private static T _instance;

    public static T Instance
    {
        get
        {
            if (_instance == null)
            {
                _instance = FindObjectOfType<T>();

                if (_instance == null)
                {
                    Debug.LogWarning("An instance of " + typeof(T) + " is added in the scene.");
                    _instance = new GameObject().AddComponent<T>();
                    _instance.name =  _instance.GetType().FullName;
                }
            }
            return _instance;
        }
    }
}