C# 类型之间有什么区别吗？和可空<类型>？
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Is there any difference between type? and Nullable<type>?
提问by MojoFilter
In C# are the nullable primitive types (i.e. bool?) just aliases for their corresponding Nullable<T>type or is there a difference between the two?
在 C# 中，可为空的原始类型（即bool?）只是它们对应Nullable<T>类型的别名，还是两者之间有区别？
采纳答案by Steve Morgan
回答by Curt Hagenlocher
A Nullable<T>is a structure consisting of a T and a bit flag indicating whether or not the T is valid. A Nullable<bool>has three possible values: true, false and null.
ANullable<T>是由 T 和指示 T 是否有效的位标志组成的结构。ANullable<bool>具有三个可能的值：true、false 和 null。
Edit:Ah, I missed the fact that the question mark after "bool" was actually part of the type name and not an indicator that you were asking a question :). The answer to your question, then, is "yes, the C# bool?is just an alias for Nullable<bool>".
编辑：啊，我错过了一个事实，即“bool”后面的问号实际上是类型名称的一部分，而不是您在问问题的指示:)。那么，您的问题的答案是“是的，C#bool?只是”的别名Nullable<bool>。
回答by Curt Hagenlocher
Null primitives are just regular primitives wrapped in Nullable. Any appearances to the contrary are just the compiler and syntactical sugar.
Null 原语只是包裹在 Nullable 中的常规原语。任何相反的现象都只是编译器和语法糖。
回答by spoulson
A boolis a value type, therefore it can't contain a NULL value. If you wrap any value type with Nullable<>, it will give it that ability. Moreover, access methods to the value change by additional properties HasValueand Value.
Abool是值类型，因此它不能包含 NULL 值。如果您用 包装任何值类型Nullable<>，它将赋予它这种能力。此外，值的访问方法通过附加属性HasValue和Value.
But to the question: Nullable<bool>and bool?are aliases.
但问题是：Nullable<bool>andbool?是别名。
回答by samjudson
There is no difference between bool? b = nulland Nullable<bool> b = null. The ?is just C# compiler syntax sugar.
bool? b = null和之间没有区别Nullable<bool> b = null。这?只是 C# 编译器语法糖。
回答by Mark Ingram
To access the value of the bool? you need to do the following:
访问布尔值？您需要执行以下操作：
bool? myValue = true;
bool hasValue = false;
if (myValue.HasValue && myValue.Value)
{
hasValue = true;
}
Note you can't just do:
请注意，您不能只做：
if (myValue)
{
hasValue = true;
}
回答by morechilli
No there is no difference. In summary:
没有没有区别。总之：
System.Boolean -> valid values : true, false
System.Boolean -> 有效值：真、假
bool -> alias for System.Boolean
bool -> System.Boolean 的别名
Nullable<bool> -> valid values : true, false, null
Nullable<bool> -> 有效值：真、假、空
bool? -> alias for Nullable<bool>
布尔？-> Nullable<bool> 的别名
Hope this helps.
希望这可以帮助。
回答by svick
I'm surprised nobody went to the source (the C# spec) yet. From §4.1.10 Nullable types:
我很惊讶还没有人去了解源代码（C# 规范）。从 §4.1.10 可空类型开始：
A nullable type is written T?, where T is the underlying type. This syntax is shorthand for System.Nullable<T>, and the two forms can be used interchangeably.
可空类型写为 T?，其中 T 是基础类型。此语法是 System.Nullable<T> 的简写，这两种形式可以互换使用。
So, no, there isn't any difference between the two forms. (Assuming you don't have any other type called Nullable<T>in any of the namespaces you use.)
所以，不，这两种形式没有任何区别。（假设您没有Nullable<T>在您使用的任何命名空间中调用任何其他类型。）
回答by AMC
No difference. Take a look here: http://msdn.microsoft.com/en-us/library/1t3y8s4s.aspx
没有不同。看看这里：http: //msdn.microsoft.com/en-us/library/1t3y8s4s.aspx
"The syntax T? is shorthand for Nullable, where T is a value type. The two forms are interchangeable."
“语法 T? 是 Nullable 的简写，其中 T 是一种值类型。这两种形式可以互换。”
