为什么C＃中不支持以下语法？ [英] Why is following syntax not supported in C#?

问题描述

IIRC在C ++中我们可以在if语句中声明变量。我们为什么不能这样做？/＃
在C＃中？

让我们看看这个例子：


object obj = GetSomeObject（） ;


if（（Customer cust = obj as Customer）！= null）

{

cust.DoStuff（）;

}

else if（（供应商支持= obj作为供应商）！= null）

{

supp .DoSomeOtherStuff（）;

}


我现在可以更好地解决这个具体的例子，但这只是一个

的例子让我知道我的意思。


问题是，目前我必须这样写：


客户服务;

供应商支持;


if（cust = obj as Customer）！= null）

{

cust.DoStuff（）;

}

else if（（supp = obj as Supplier）！= null）

{

supp.DoSomeOtherStuff（）;

}


这会不必要地将两个变量的可见性扩展到外部

范围。

什么你是否考虑过这个想法？

IIRC in C++ we can declare variables in if statements. Why can''t we do that
in C#?
Lets see that example:

object obj = GetSomeObject();

if ((Customer cust = obj as Customer)!=null)
{
cust.DoStuff();
}
else if ((Supplier supp = obj as Supplier )!=null)
{
supp.DoSomeOtherStuff();
}

I now that that specific example could be solved better but this is just an
example to give you the idea what I mean.

The problem is that at the moment I have to write it like that:

Customer cust;
Supplier supp;

if (cust = obj as Customer)!=null)
{
cust.DoStuff();
}
else if ((supp = obj as Supplier )!=null)
{
supp.DoSomeOtherStuff();
}

this unnecessarily expands the visibility of both variables to the outer
scope.
What do you think about that idea?

推荐答案

尝试（客户）obj将你的obj投射到客户类型。 As表示As。关键字是

VB。这样的事情（未经测试，但它可能会指向你一般的

方向）：


if（（Customer cust =（Customer）obj）！= null）

{

cust.DoStuff（）;

}

else if（（供应商支持=（供应商）obj）！= null）

{

supp.DoSomeOtherStuff（）;

}


" cody" <德******** @ gmx.de>写在消息中

新闻：ef ************** @ TK2MSFTNGP10.phx.gbl ...

Try (Customer)obj to cast your obj to Customer type. The "As" keyword is
VB. Something like this (untested, but it might point you in the general
direction):

if ((Customer cust = (Customer)obj)!=null)
{
cust.DoStuff();
}
else if ((Supplier supp = (Supplier)obj)!=null)
{
supp.DoSomeOtherStuff();
}

"cody" <de********@gmx.de> wrote in message
news:ef**************@TK2MSFTNGP10.phx.gbl...

IIRC in C ++我们可以在if语句中声明变量。我们为什么不能在C＃中使用
？
让我们看一下这个例子：

对象obj = GetSomeObject（）;
if（（Customer cust = obj as Customer）！= null）
{
cust.DoStuff（）;
}
if if（（供应商supp = obj as Supplier） ！= null）
{
supp.DoSomeOtherStuff（）;
}
我现在可以更好地解决这个具体的例子，但这只是
一个例子让你明白我的意思。

问题是，目前我必须这样写：

客户委托;
供应商支持;

if（cust = obj as Customer）！= null）
{
cust.DoStuff（）;
}
否则if（（supp = obj as Supplier）！= null）

supp.sDoSomeOtherStuff（）;
}
这会不必要地扩大两个变量的可见性外部
范围。
你对这个想法怎么看？

IIRC in C++ we can declare variables in if statements. Why can''t we do
that
in C#?
Lets see that example:

object obj = GetSomeObject();

if ((Customer cust = obj as Customer)!=null)
{
cust.DoStuff();
}
else if ((Supplier supp = obj as Supplier )!=null)
{
supp.DoSomeOtherStuff();
}

I now that that specific example could be solved better but this is just
an
example to give you the idea what I mean.

The problem is that at the moment I have to write it like that:

Customer cust;
Supplier supp;

if (cust = obj as Customer)!=null)
{
cust.DoStuff();
}
else if ((supp = obj as Supplier )!=null)
{
supp.DoSomeOtherStuff();
}

this unnecessarily expands the visibility of both variables to the outer
scope.
What do you think about that idea?

你好Cody，

你可以使用''是''关键字


object obj = GetSomeObject（）;


if（obj is Customer）

{

（（客户）obj）.DoStuff（）;

}

else if（obj是供应商）

{

（（供应商）obj）.DoSomeOtherStuff（）;

}


它不会''但就像你的C ++代码一样。



2005年5月26日星期四15:09:14 +0200，cody< de ******* *@gmx.de>写道：

Hi Cody,

You can use the ''is'' keyword

object obj = GetSomeObject();

if(obj is Customer)
{
((Customer)obj).DoStuff();
}
else if(obj is Supplier)
{
((Supplier)obj).DoSomeOtherStuff();
}

It wouldn''t be exactly as your C++ code though.


On Thu, 26 May 2005 15:09:14 +0200, cody <de********@gmx.de> wrote:

IIRC在C ++中我们可以在if语句中声明变量。为什么我们不能在C＃中这样做？
让我们看看那个例子：

对象obj = GetSomeObject（）;

if（（客户cust = obj as Customer）！= null）
{
cust.DoStuff（）;
}
if if（（供应商supp = obj as Supplier）！= null）
{
supp.DoSomeOtherStuff（）;
}
我现在可以更好地解决这个具体的例子，但这只是一个给出的例子你的想法是什么意思。

问题是，目前我必须这样写：

客户委托;
供应商支持;

if（cust = obj as Customer）！= null）
{
cust.DoStuff（）;
}
if if（（supp = obj as供应商）！= null）
这一点不必要地将两个变量的可见性扩展到外部范围。
你怎么看待这个想法？

IIRC in C++ we can declare variables in if statements. Why can''t we do that
in C#?
Lets see that example:

object obj = GetSomeObject();

if ((Customer cust = obj as Customer)!=null)
{
cust.DoStuff();
}
else if ((Supplier supp = obj as Supplier )!=null)
{
supp.DoSomeOtherStuff();
}

I now that that specific example could be solved better but this is just an
example to give you the idea what I mean.

The problem is that at the moment I have to write it like that:

Customer cust;
Supplier supp;

if (cust = obj as Customer)!=null)
{
cust.DoStuff();
}
else if ((supp = obj as Supplier )!=null)
{
supp.DoSomeOtherStuff();
}

this unnecessarily expands the visibility of both variables to the outer
scope.
What do you think about that idea?

-

快乐的编码！

Morten Wennevik [C＃ MVP]

--
Happy coding!
Morten Wennevik [C# MVP]

Fist，cast抛出异常而不是我的代码的意图，第二个

在C＃中支持as关键字* * 。它没有扔，而是返回

null。

Michael C＃ <豪*** @ boutdat.com> schrieb im Newsbeitrag

新闻：#D ************** @ TK2MSFTNGP12.phx.gbl ...

Fist, casting throws an exception which is not the intent of my code, second
the as keyword *is* supported in C#. It doesn''t throw but instead returns
null.
"Michael C#" <ho***@boutdat.com> schrieb im Newsbeitrag
news:#D**************@TK2MSFTNGP12.phx.gbl...

试试（客户） obj将您的obj转换为Customer类型。 As表示As。关键字是
VB。这样的事情（未经测试，但它可能指向你一般的方向）：

if（（Customer cust =（Customer）obj）！= null）
{
cust.DoStuff（）;
}
否则if（（供应商支持=（供应商）obj）！= null）
{
supp.DoSomeOtherStuff（）;
}

cody <德******** @ gmx.de>在消息中写道
新闻：ef ************** @ TK2MSFTNGP10.phx.gbl ...

Try (Customer)obj to cast your obj to Customer type. The "As" keyword is
VB. Something like this (untested, but it might point you in the general
direction):

if ((Customer cust = (Customer)obj)!=null)
{
cust.DoStuff();
}
else if ((Supplier supp = (Supplier)obj)!=null)
{
supp.DoSomeOtherStuff();
}

"cody" <de********@gmx.de> wrote in message
news:ef**************@TK2MSFTNGP10.phx.gbl...

IIRC在C ++中我们可以在if中声明变量声明。我们为什么不能在C＃中使用
？
让我们看一下这个例子：

对象obj = GetSomeObject（）;
if（（Customer cust = obj as Customer）！= null）
{
cust.DoStuff（）;
}
if if（（供应商supp = obj as Supplier） ！= null）
{
supp.DoSomeOtherStuff（）;
}
我现在可以更好地解决这个具体的例子，但这只是
一个例子让你明白我的意思。

问题是，目前我必须这样写：

客户委托;
供应商支持;

if（cust = obj as Customer）！= null）
{
cust.DoStuff（）;
}
否则if（（supp = obj as Supplier）！= null）

supp.sDoSomeOtherStuff（）;
}
这会不必要地扩大两个变量的可见性外部
范围。
您如何看待这个想法？

IIRC in C++ we can declare variables in if statements. Why can''t we do
that
in C#?
Lets see that example:

object obj = GetSomeObject();

if ((Customer cust = obj as Customer)!=null)
{
cust.DoStuff();
}
else if ((Supplier supp = obj as Supplier )!=null)
{
supp.DoSomeOtherStuff();
}

I now that that specific example could be solved better but this is just
an
example to give you the idea what I mean.

The problem is that at the moment I have to write it like that:

Customer cust;
Supplier supp;

if (cust = obj as Customer)!=null)
{
cust.DoStuff();
}
else if ((supp = obj as Supplier )!=null)
{
supp.DoSomeOtherStuff();
}

this unnecessarily expands the visibility of both variables to the outer
scope.
What do you think about that idea?

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