为什么可空＆LT; T＆GT; HasValue属性不是空值抛出NullReferenceException异常？ [英] Why does Nullable<T> HasValue property not throw NullReferenceException on Nulls?

问题描述

考虑以下code：

DateTime? ndate = null;
Console.WriteLine(ndate.HasValue);

我本来期望一个NullReferenceException，但hasVa​​lue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hasVa​​lue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?

推荐答案

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<一个href="http://msdn.microsoft.com/en-us/library/b3h38hb0.aspx"><$c$c>Nullable<DateTime>,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.

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