Kotlin申请String无法正常工作 [英] Kotlin apply on String not working as expected

问题描述

我正在尝试使用kotlin的所有功能，但似乎其中一些功能无法正常工作，或者可能是我的错.

I am trying to use all features of kotlin, but seems not of them are working, or may be it's my fault.

因此，从apply到String无效.示例:

So, apply to String not work. Example:

val str = someStr.apply {
    toUpperCase()
    if (contains("W")) replace("W", "w")
}

输入-> xywz

Input -> xywz

输出-> xywz

预期-> XYwZ

Java风格:

val str = it.text().toString().toUpperCase()
if (str.contains("W")) str.replace("W", "w")

输入-> xywz

Input -> xywz

输出-> XYwZ

预期-> XYwZ

我做错什么了吗?

推荐答案

toUpperCase()返回字符串的副本(字符串是不可变的).因此，您需要将返回的值存储为apply()中的独立(不是最后)语句，它会丢失.

toUpperCase() returns a copy of the string (strings are immutable). So you need to store the returned value, as a stand-alone (not last) statement inside apply() it is lost.

此外，如果返回表达式，则不能在没有else的情况下使用if.您甚至不需要contains().

Also, you can't use if without else, if you return an expression. The contains() is not even needed in your case.

您可能想做的是直接调用toUpperCase()和replace():

What you probably would like to do is call toUpperCase() and replace() directly:

val str = someStr.toUpperCase().replace("W", "w")

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