C# 使用“+”运算符的字符串连接
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String Concatenation using '+' operator
提问by NoviceProgrammer
Looking at the stringclass metadata, I only see the operators ==and !=overloaded. So how is it able to perform concatenation for the '+' operator?
查看string类元数据，我只看到运算符==和!=重载。那么它如何能够为 ' +' 运算符执行连接？
Edit:
编辑：
Some interesting notes from Eric Lippert on string concatenation:
Eric Lippert 关于字符串连接的一些有趣笔记：
There is also a super article from Joel referred in part 2 (http://www.joelonsoftware.com/articles/fog0000000319.html)
还有一篇来自 Joel 的超级文章在第 2 部分中提到（http://www.joelonsoftware.com/articles/fog0000000319.html）
采纳答案by Jon Skeet
It doesn't - the C# compiler does :)
它没有 - C# 编译器有 :)
So this code:
所以这段代码：
string x = "hello";
string y = "there";
string z = "chaps";
string all = x + y + z;
actually gets compiled as:
实际上被编译为：
string x = "hello";
string y = "there";
string z = "chaps";
string all = string.Concat(x, y, z);
(Gah - intervening edit removed other bits accidentally.)
（Gah - 干预编辑意外删除了其他位。）
The benefit of the C# compiler noticing that there are multiple string concatenations here is that you don't end up creating an intermediate string of x + ywhich then needs to be copied again as part of the concatenation of (x + y)and z. Instead, we get it all done in one go.
C# 编译器注意到这里有多个字符串连接的好处是，您最终不会创建一个中间字符串x + y，然后需要再次复制它作为(x + y)和连接的一部分z。相反，我们一次性完成所有工作。
EDIT: Note that the compiler can'tdo anything if you concatenate in a loop. For example, this code:
编辑：请注意，如果您在循环中连接，编译器将无法执行任何操作。例如，这段代码：
string x = "";
foreach (string y in strings)
{
x += y;
}
just ends up as equivalent to:
最终等同于：
string x = "";
foreach (string y in strings)
{
x = string.Concat(x, y);
}
... so this doesgenerate a lot of garbage, and it's why you should use a StringBuilderfor such cases. I have an article going into more details about the twowhich will hopefully answer further questions.
...所以这确实会产生很多垃圾，这就是为什么你应该StringBuilder在这种情况下使用 a 。我有一篇文章详细介绍了这两者，希望能回答更多问题。
