public struct Maybe<T> : IEquatable<Maybe<T>> {
        private T value;
        private bool has_value;
        private static bool _isnullable = typeof(T).IsNullable();

        public Maybe (T value)
        {
            if (value == null)
            {
                if (!_isnullable)
                {
                    throw new ArgumentNullException("value");
                }
            }

            this.value = value;
            has_value  = true;
        }