为什么可空＆LT; T＆GT; HasValue属性不是空值抛出NullReferenceException异常？
考虑以下code：
DateTime? ndate = null;
Console.WriteLine(ndate.HasValue);
我本来期望一个NullReferenceException，但hasValue的确实将返回false。然而，由于ndate为null，如何属性调用成功，因为没有对象调用的财产hasValue的？
I would have expected a NullReferenceException, but HasValue will indeed return false. However, since ndate is null, how does the property invocation succeed, since there is no object to invoke the property HasValue on?
从技术上讲，ndate不为空 - 它是值类型，与它的值指定为空
Technically, "ndate" is not null - it is a value type, with it's value specified as being null.
当你写日期时间？，这仅仅是速记Nullable<DateTime>$c$c>,这是一个结构。有没有办法让这个在技术上是无效的，因为它不是一个引用类型。
When you write DateTime?, this is just shorthand for Nullable<DateTime>, which is a struct. There is no way for this to technically be null, since it's not a reference type.