为什么C#中的DateTime不允许为null? [英] Why is null not allowed for DateTime in C#?
问题描述
为什么在C#中不允许将null分配给DateTime?这是如何实施的?可以使用此功能使您自己的类不可为空吗?
示例:
string stringTest = null; // Okay
DateTime dateTimeTest = null; // Compile error
我知道我可以在C#2.0中使用DateTime?将null分配给dateTimeTest，并且可以使用解决方案
DateTime是值类型(struct)，其中-string是引用类型(class等).那是关键的区别.引用始终可以为null；一个值不能(除非它使用Nullable<T>-即DateTime?)，尽管它可以为零(DateTime.MinValue)，通常将其解释为与null相同(尤其是1.1)./p>
Why it is not allowed to assign null to a DateTime in C#? How has this been implemented? And can this feature be used to make your own classes non-nullable?
Example:
string stringTest = null; // Okay
DateTime dateTimeTest = null; // Compile error
I know that I can use DateTime? in C# 2.0 to allow null to be assigned to dateTimeTest and that I could use Jon Skeet's NonNullable class on my string to get a run time error on the assignment of stringTest. I'm just wondering why the two types behave differently.
DateTime is a value-type (struct), where-as string is a reference-type (class etc). That is the key difference. A reference can always be null; a value can't (unless it uses Nullable<T> - i.e. DateTime?), although it can be zero'd (DateTime.MinValue), which is often interpreted as the same thing as null (esp. in 1.1).
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