如果没有替代内容，String.Replace()是否会创建一个新字符串? [英] Does String.Replace() create a new string if there's nothing to replace?

问题描述

例如:

public string ReplaceXYZ(string text)
{
    string replacedText = text;

    replacedText = replacedText.Replace("X", String.Empty);
    replacedText = replacedText.Replace("Y", String.Empty);
    replacedText = replacedText.Replace("Z", String.Empty);

    return replacedText;
}

如果即使对于不包含"X"，"Y"或"Z"的字符串也要调用"ReplaceXYZ"，那么每次都会创建3个新字符串吗?

If I were to call "ReplaceXYZ" even for strings that do not contain "X", "Y", or "Z", would 3 new strings be created each time?

我在我们的一个项目中发现了与此类似的代码.当它循环遍历大量字符串时，会反复调用它.

I spotted code similar to this in one of our projects. It's called repeatedly as it loops through a large collection of strings.

推荐答案

如果没有可替换的内容，它不会返回新实例:

It does not return a new instance if there is nothing to replace:

string text1 = "hello world", text2 = text1.Replace("foo", "bar");
bool referenceEqual = object.ReferenceEquals(text1, text2);

执行该代码后，将referenceEqual设置为true.

After that code executes, referenceEqual is set to true.

更好的是，此行为已记录:

如果在当前实例中未找到oldValue，则该方法将不变地返回当前实例.

If oldValue is not found in the current instance, the method returns the current instance unchanged.

否则，这将取决于实现，并且将来可能会改变.

Otherwise, this would be implementation-dependent and could change in the future.

请注意，有类似的记录了针对string值调用Substring(0)的优化:

Note that there is a similar, documented optimization for calling Substring(0) on a string value:

如果startIndex等于零，则该方法不变地返回原始字符串

If startIndex is equal to zero, the method returns the original string unchanged

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