为什么;;允许在局部变量声明之后，而不是在字段声明之后?

I saw this weird behaviour and I wonder if there's a reasonable explanation for this:

我看到了这种奇怪的行为，我怀疑是否有合理的解释:

When I put by ( by accident) an additional/extra semicolon in a function's local variable like:

当我(意外地)在函数的局部变量中添加/额外分号:

public void MyMethod ()
{
    int a = 1;;
    Console.WriteLine(a); //dummy 
}

It does compile but it shows that it's redundant.

它确实编译了，但它显示它是冗余的。

But when I did that with fields (also by accident) , I got an error (compilation) :

但是，当我用字段(也意外地)做这些时，我得到了一个错误(编译):

Question

问题

Is there any reason for this restrictiveness in fields ?

在这些领域中存在这种限制的原因吗?

^{Nb I already know the other restrictiveness thing for not allowing var with fields. But here it's something different.}

Nb我已经知道不允许var和字段的其他限制。但这里有一些不同的东西。

5 个解决方案

#1

; alone is a statement (empty statement), but only declaration statements are allowed in the body of a class; other kinds of statement can only appear in the body of a method.

;单独是一个语句(空语句)，但只允许在类的主体中声明声明语句;其他类型的语句只能出现在方法的主体中。

#2

; itself is an empty statement. And in class scope only the declaration statements are allowed.The class body is defined in C# Specification 5.0, §10.1.6 Class Body

;它本身就是一个空的语句。在类范围内，只允许声明语句。类主体是在c#规范5.0中定义的。

class-body:
{   class-member-declarations   }

For example you can't initialize a field in a separate statement:

例如，您不能在单独的语句中初始化字段:

class Foo 
{
    int x = 2; // this is allowed 
    x = 5; // this is not
}

So you can only declare fields and other members but you can't use other statements in a class body.

因此只能声明字段和其他成员，但不能在类主体中使用其他语句。

#3

It is not part of local variable declaration, it's a statement by itself, as indicated by Thomas.

它不是局部变量声明的一部分，它本身就是一个声明，正如Thomas所指出的那样。

This is valid:

这是有效的:

public void MyMethod ()
{
    ;;;
    int a = 1;


    ;
    Console.WriteLine(a); //dummy 
    ;;
}

The idea of semi-colon statement is to allow such constructs:

分号声明的思想是允许这样的结构:

while(mycondition) ;

It does not make sense to allow it in in the body of class, it brings no extra value.

允许它在类的主体中是没有意义的，它不会带来额外的价值。

TLDR; this has nothing to do with variable/field declaration

TLDR;这与变量/字段声明无关。

You might want to take a look at this thread too: When do you use scope without a statement in C#?

您可能还想看一下这个线程:在c#中，什么时候使用范围而没有声明?

It is kind of similiar, but not completely, it will help you to understand why

这是一种相似的，但不是完全的，它将帮助你理解为什么。

int a = 1;;;

int = 1;;;

is valid.

是有效的。

#4

In the first case the compiler sees a no-op statement. It doesn't matter that the second ; comes after a variable declaration.

在第一个例子中，编译器看到一个无op的语句。第二个问题无关紧要;在变量声明之后。

In the second case the compiler sees an attempt to create an empty declaration which isn't allowed.

在第二种情况下，编译器看到试图创建一个不允许的空声明。

#5

-4

Inside the body of a function the redundant ; is an empty statement but in the class declaration is an undeclared field and it not allowed.

在一个函数的内部是冗余的;是空语句，但在类声明中是未声明的字段，不允许。

#1