using System;

namespace VCommon
{
    /// <summary>
    /// 惰性初始化包裹, 线程安全
    /// </summary>
    public class LazyHolder<T> where T : class
    {
        private readonly object _lock = new object();
        private readonly Func<T> _initFunc;

        private T _heldInstance;

        public LazyHolder(Func<T> initFunc) => _initFunc = initFunc;

        public T Instance
        {
            get
            {
                if (_heldInstance == null)
                {
                    lock (_lock)
                    {
                        if (_heldInstance == null)
                        {
                            _heldInstance = _initFunc();
                        }
                    }
                }

                return _heldInstance;
            }
        }
    }
}