??结构上的“新”和“受保护”修饰符?? [英] ?? 'new' and 'protected' Modifiers on Structs ??

问题描述

大家好，


有没有人看过C＃规范的第18.1.1节？它表示''new''和

''protected''是结构声明的有效修饰符。首先，

''protected''如何在结构上有效，因为结构不能被继承？

编译器会出现错误（正如我预期的那样），如果您尝试这样做：


protected struct MyStruct {}


所以当我说''protected''是一个有效的

结构修饰符时，我想知道规格是否错误。


关于第18.1.1节的第二点是它表示''new''是结构上的一个允许修饰符。实际上，18.1.1表示，结构声明的修饰符

与类

声明的含义相同，请读者参阅第17.1节。 1上课声明

修饰符。


我查看了第17.1.1节，果然，它说：


"嵌套类允许使用new修饰符。

它指定该类以相同的名称隐藏继承的成员

，如第17.2.2节所述。它是一个编译时错误，新修饰符在一个不是嵌套类声明的类声明中出现

。


我的测试表明在类或结构声明中不允许''new''

（嵌套与否）。根据规范（第17.1.1节），这似乎是''新'应该如何用作类

修饰符：


class MyClass {

public virtual int M（）{return 1; }

}


class Outer {

new class Inner：MyClass {// ERROR on''new''修饰符

public new int M（）{return 2; }

}

}


上面的代码给出了内部声明的警告。

所以，我离开基地了吗？ 18.1.1

和17.1.1是否有问题？


谢谢

-

Tom Baxter

解决方案

Tom Baxter写道：

大家好，


有没有人看过C＃规范的第18.1.1节？它表示''new''

和''protected''是结构声明的有效修饰符。首先，

如何保护在结构上有效，因为结构不能被继承？

编译器发出错误（正如我预期的那样）你试试这个：


protected struct MyStruct {}


所以当我说保护时，我想知道规范是否错误''是一个

有效的struct-modifier。


第18.1.1节的第二点是它表示''new''是一个允许修饰符。实际上，18.1.1表示，结构声明的

修饰符与

类声明的含义相同，请读者参阅第17.1节。 1上课

声明修饰符。


我查看了第17.1.1节，果然，它说：


"嵌套类允许使用new修饰符。

它指定该类以相同的名称隐藏继承的成员

，如第17.2.2节所述。它是一个编译时错误，新修饰符在一个不是嵌套类声明的类声明中出现

。


我的测试表明，'new''不允许在类或结构上

声明（嵌套与否）。根据规范（第17.1.1节），这似乎应该是''新'应该如何使用

作为类修饰符：


class MyClass {

public virtual int M（）{return 1; }

}


class Outer {

new class Inner：MyClass {// ERROR on''new''修饰符

public new int M（）{return 2; }

}

}


上面的代码给出了内部声明的警告。

我想如果你改变你的定义来实际隐藏一个成员（M）你将会消除那个错误。

class MyClass

{

public virtual int M（）{return 1; }

}


class Outer：MyClass

{

公共新类M：MyClass < br $>
{

}

}


class C2：MyClass

{

公共新结构M

{

}

}

并在受保护上侧面 - 它再次涉及子类的内容

包含类 - 即


公共类BaseClass {

void TestBase（） {

NestedStruct ns;

}

private struct NestedStruct {int a;}

}

public class SubClass：BaseClass {

void TestSub（）{

NestedStruct ns; // **错误

}

}


以上是非法的，因为SubClass看不到BaseClass.NestedStruct

（因为它是私人的）;但是，更改NestedStruct是受保护的，

和任何BaseClass子类现在都能看到它。


Marc

谢谢，Marc !!我很抱歉！

" Marc Gravell" < ma ********** @ gmail.comwrote in message

news：11 ******************** **@50g2000hsm.googlegro ups.com ...

并在受保护上侧面 - 它再次涉及子类的内容

包含类 - 即


公共类BaseClass {

void TestBase（） {

NestedStruct ns;

}

private struct NestedStruct {int a;}

}

public class SubClass：BaseClass {

void TestSub（）{

NestedStruct ns; // **错误

}

}


以上是非法的，因为SubClass看不到BaseClass.NestedStruct

（因为它是私人的）;但是，更改NestedStruct是受保护的，

和任何BaseClass子类现在可以看到它。


Marc

-

Tom Baxter

Hi everyone,

Has anyone looked at section 18.1.1 of the C# spec? It indicates ''new'' and
''protected'' are valid modifiers on struct declarations. First, how can
''protected'' be valid on a struct, since structs cannot be inherited? The
compiler gives an error (as I expect it should) if you try this:

protected struct MyStruct {}

so I''m wondering if the spec is wrong when it says ''protected'' is a valid
struct-modifier.

The second point about section 18.1.1 is that it indicates ''new'' is an
allowable modifier on a struct. Actually, 18.1.1 indicates, "The modifiers
of a struct declaration have the same meaning as those of a class
declaration", referring the reader to section 17.1.1 on class declaration
modifiers.

I looked at section 17.1.1 and sure enough, it says:

"The new modifier is permitted on nested classes.
It specifies that the class hides an inherited member
by the same name, as described in section 17.2.2. It
is a compile-time error for the new modifier to appear
on a class declaration that is not a nested class declaration."

My testing indicates ''new'' is not allowed on class nor struct declarations
(nested or not). It seems this is how ''new'' should be used as a class
modifier, according to the spec (sec. 17.1.1):

class MyClass {
public virtual int M() { return 1; }
}

class Outer {
new class Inner : MyClass { // ERROR on ''new'' modifier
public new int M() { return 2; }
}
}

The above code gives a warning on the declaration of Inner.

So, am I way off base here? Is there something wrong with sections 18.1.1
and 17.1.1?

Thanks
--
Tom Baxter

解决方案

Tom Baxter wrote:

Hi everyone,

Has anyone looked at section 18.1.1 of the C# spec? It indicates ''new''
and ''protected'' are valid modifiers on struct declarations. First, how
can ''protected'' be valid on a struct, since structs cannot be inherited?
The compiler gives an error (as I expect it should) if you try this:

protected struct MyStruct {}

so I''m wondering if the spec is wrong when it says ''protected'' is a
valid struct-modifier.

The second point about section 18.1.1 is that it indicates ''new'' is an
allowable modifier on a struct. Actually, 18.1.1 indicates, "The
modifiers of a struct declaration have the same meaning as those of a
class declaration", referring the reader to section 17.1.1 on class
declaration modifiers.

I looked at section 17.1.1 and sure enough, it says:

"The new modifier is permitted on nested classes.
It specifies that the class hides an inherited member
by the same name, as described in section 17.2.2. It
is a compile-time error for the new modifier to appear
on a class declaration that is not a nested class declaration."

My testing indicates ''new'' is not allowed on class nor struct
declarations (nested or not). It seems this is how ''new'' should be used
as a class modifier, according to the spec (sec. 17.1.1):

class MyClass {
public virtual int M() { return 1; }
}

class Outer {
new class Inner : MyClass { // ERROR on ''new'' modifier
public new int M() { return 2; }
}
}

The above code gives a warning on the declaration of Inner.

I think if you change your definition to actually hide a member (M) you
will remove that error.
class MyClass
{
public virtual int M() { return 1; }
}

class Outer : MyClass
{
public new class M : MyClass
{
}
}

class C2 : MyClass
{
public new struct M
{
}
}

And on the "protected" side - it again relates to things that subclass
the containing class - i.e.

public class BaseClass {
void TestBase() {
NestedStruct ns;
}
private struct NestedStruct { int a;}
}
public class SubClass : BaseClass {
void TestSub() {
NestedStruct ns; // **ERROR
}
}

The above is illegal, since SubClass cannot see BaseClass.NestedStruct
(since it is private); however, change NestedStruct to be protected,
and any sublasses of BaseClass can now see it.

Marc

Thanks, Marc!! I appeciate!
"Marc Gravell" <ma**********@gmail.comwrote in message
news:11**********************@50g2000hsm.googlegro ups.com...

And on the "protected" side - it again relates to things that subclass
the containing class - i.e.

public class BaseClass {
void TestBase() {
NestedStruct ns;
}
private struct NestedStruct { int a;}
}
public class SubClass : BaseClass {
void TestSub() {
NestedStruct ns; // **ERROR
}
}

The above is illegal, since SubClass cannot see BaseClass.NestedStruct
(since it is private); however, change NestedStruct to be protected,
and any sublasses of BaseClass can now see it.

Marc

--
Tom Baxter

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