Framwork/Assets/Scripts/Base/ManagerBase.cs

using System;

namespace HK
{
    internal class ManagerBase<T> where T : new()
    {
        private static T _instance;

        public static T Instance
        {
            get
            {
                if (_instance == null)
                {
                    _instance = new T();
                }

                return _instance;
            }
        }
    }
}