GenericSingleton

using UnityEngine;
using System.Collections;

public class GlobalManager<T> : MonoBehaviour {
    [SerializeField]
    bool _persistent = false;

    private static T _instance;
    public static bool IsInstantianted { get { return _instance != null; } }
    protected virtual void Init() {}

    public static T Instance {
        get {
            if (_instance != null)
                return _instance;
            else {
                string errorMessage = typeof(T).Name + " is not attached to a GameObject or inactive.";
                Debug.LogError(errorMessage);
                throw new System.NullReferenceException(errorMessage);
            }
        }
    }

    void Awake() {
        if (Instantiation())
            Init();
    }

    bool Instantiation() {
        if (IsInstantianted) {
            Debug.LogWarning("Only one " + typeof(T) + " is allowed, destroying " + gameObject.name);
            Destroy(gameObject);
            return false;
        }
        _instance = (T) (object) this;

        if (_persistent)
            DontDestroyOnLoad(this);
        return true;
    }
}