blocks|key|2993417|text|它实际上只是一种编码风格。编译器为两个变体生成完全相同的结果。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2993418|有关性能问题，另请参阅此处：|2993419|2993420|Will+using+'var'+affect+performance?|unordered-list-item|offset|length|2993421|2993422|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/356846/c-var-vs-specific-type-performance^0|0|0|0|0|10|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|U|8|@]|9|@]|A|$]]|$1|E|3|F|5|G|7|V|8|@]|9|@$H|W|I|X|1|Y]]|A|$]]|$1|J|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|10|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

It's really just a coding style. The compiler generates the exact same for both variants.

See also here for the performance question:

<ul>
<li><a href="https://stackoverflow.com/questions/356846/c-var-vs-specific-type-performance">Will using &#39;var&#39; affect performance?</a></li>
</ul>

blocks|key|285552|text|你说的“警告”到底是什么意思？我经常看到它给出一个提示，你可能想使用var，但没有什么比警告更刺耳的了。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|285553|使用var没有性能差异-代码被编译成相同的IL。潜在的好处在于可读性-如果你已经在赋值的RHS上明确了变量的类型(例如，通过强制转换或构造函数调用)，那么在LHS上也有它的好处在哪里？不过，这是个人喜好。|285554|如果您不希望R#建议使用var，只需更改选项即可。关于ReSharper的一件事:它是非常可配置的:)|285555|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

When you say "by warnings" what exactly do you mean? I've usually seen it giving a hint that you may want to use var, but nothing as harsh as a warning.

There's no performance difference with var - the code is compiled to the same IL. The potential benefit is in readability - if you've already made the type of the variable crystal clear on the RHS of the assignment (e.g. via a cast or a constructor call), where's the benefit of also having it on the LHS? It's a personal preference though.

If you don't want R# suggesting the use of var, just change the options. One thing about ReSharper: it's very configurable :)

blocks|key|2993594|text|在这种情况下，它只是编码风格。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2993595|只有在处理匿名类型时才需要使用var。|offset|length|style|CODE|2993596|在其他情况下，这是一个品味问题。|2993597|entityMap^0|0|F|3|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@$D|N|E|O|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|P|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|K|$]]

In this case it is just coding style. 

Use of <code>var</code> is only necessary when dealing with anonymous types. 
In other situations it's a matter of taste.

blocks|key|285601|text|正如其他人所说，当您使用以下任一选项时，编译后的代码(IL)没有区别：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|285602|var+x1+=+new+object();
object+x2+=+new+object;|code-block|syntax|javascript|285603|我想Resharper之所以警告你，是因为在我看来，读第一个例子比读第二个例子更容易。此外，有什么必要重复两次类型的名称呢？|285604|考虑以下几点，你就会明白我的意思：|285605|KeyValuePair<string,+KeyValuePair<string,+int>>+y1+=+new+KeyValuePair<string,+KeyValuePair<string,+int>>("key",+new+KeyValuePair<string,+int>("subkey",+5));|285606|取而代之的是它更容易阅读：|285607|var+y2+=+new+KeyValuePair<string,+KeyValuePair<string,+int>>("key",+new+KeyValuePair<string,+int>("subkey",+5));|285608|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|W|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

As the others have said, there is no difference in the compiled code (IL) when you use either of the following:

<pre><code>var x1 = new object();
object x2 = new object;
</code></pre>

I suppose Resharper warns you because it is [in my opinion] easier to read the first example than the second. Besides, what's the need to repeat the name of the type twice?

Consider the following and you'll get what I mean:

<pre><code>KeyValuePair&lt;string, KeyValuePair&lt;string, int&gt;&gt; y1 = new KeyValuePair&lt;string, KeyValuePair&lt;string, int&gt;&gt;("key", new KeyValuePair&lt;string, int&gt;("subkey", 5));
</code></pre>

It's way easier to read this instead:

<pre><code>var y2 = new KeyValuePair&lt;string, KeyValuePair&lt;string, int&gt;&gt;("key", new KeyValuePair&lt;string, int&gt;("subkey", 5));
</code></pre>

<blockquote>
 Possible Duplicate: 
 <a href="https://stackoverflow.com/questions/737835/resharper-and-var">ReSharper and var</a> 
</blockquote>



After I have installed ReSharper it demands(by warnings) that I use var whenever possible, for example

<pre><code>UnhandledExceptionEventArgs ue = (UnhandledExceptionEventArgs) t;
</code></pre>

ReSharper wants to turn it into

<pre><code>var ue = (UnhandledExceptionEventArgs) t;
</code></pre>

I like the first version better, is there any reason to prefer var? better performance? anything? or is it just a code style?

Why should I use var instead of a type?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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 可能重复：在我安装了ReSharper之后，它(通过警告)要求我尽可能使用var，例如UnhandledExceptionEventArgs ue = (UnhandledExceptionEventArgs) t;ReSharper想把它变成var ue = (UnhandledExceptionEventArgs...

问为什么我应该使用var而不是一个类型？
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问为什么我应该使用var而不是一个类型？
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