字符串实习？

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第二个ReferenceEquals调用返回false。为什么不对s4中的字符串进行实习？ （我不在乎StringBuilder相对于字符串连接的优势。）

The second ReferenceEquals call returns false. Why isn't the string in s4 interned? (I don't care about the advantages of StringBuilder over string concatenation.)

string s1 = "tom"; string s2 = "tom"; Console.Write(object.ReferenceEquals(s2, s1)); //true string s3 = "tom"; string s4 = "to"; s4 += "m"; Console.Write(object.ReferenceEquals(s3, s4)); //false

当我这样做时 String.Intern（s4）; ，我仍然是假的。

When I do String.Intern(s4);, I still get false.

在这里，s3和s4都被拘留了，但是它们的引用不相等？

Here, both s3 and s4 are interned but their references are not equal?

string s3 = "tom"; string s4 = "to"; s4 += "m"; String.Intern(s4); Console.WriteLine(s3 == s4); //true Console.WriteLine(object.ReferenceEquals(s3, s4)); //false Console.WriteLine(string.IsInterned(s3) != null); //true (s3 is interned) Console.WriteLine(string.IsInterned(s4) != null); //true (s4 is interned)

推荐答案

s4 被拘留。但是，当您执行 s4 + = m; 时，您创建了一个不会被插入的新字符串，因为它的值不是字符串文字，而是a的结果字符串串联操作。结果， s3 和 s4 是在两个不同的内存位置中的两个不同的字符串实例。

The string in s4 is interned. However, when you execute s4 += "m";, you have created a new string that will not be interned as its value is not a string literal but the result of a string concatenation operation. As a result, s3 and s4 are two different string instances in two different memory locations.

有关字符串实习的更多信息，请参见此处，特别是在最后一个示例中。当您执行 String.Intern（s4）时，您确实在对字符串进行了内部检查，但是您仍未在这两个被内部检查的字符串之间执行引用相等性测试。 String.Intern 方法返回被插入的字符串，因此您需要执行以下操作：

For more information on string interning, look here, specifically at the last example. When you do String.Intern(s4), you are indeed interning the string, but you are still not performing a reference equality test between those two interned strings. The String.Intern method returns the interned string, so you would need to do this:

string s1 = "tom"; string s2 = "tom"; Console.Write(object.ReferenceEquals(s2, s1)); //true string s3 = "tom"; string s4 = "to"; s4 += "m"; Console.Write(object.ReferenceEquals(s3, s4)); //false string s5 = String.Intern(s4); Console.Write(object.ReferenceEquals(s3, s5)); //true