C# dotnet WeakLazy 弱引用的延迟初始化实现方法

    class WeakLazy<T> where T : class, new()
    {
        WeakReference<T> _instance = new WeakReference<T>(null);
        public T Value
        {
            get
            {
                lock (_instance)
                {
                    T value;
                    if (!_instance.TryGetTarget(out value))
                    {
                        value = new T();
                        _instance.SetTarget(value);
                    }
                    return value;
                }
            }
        }
    }