Kotlin - Issue Extending Kotlin String Class-CodePudding

I am currently trying to extend Kotlins String class with a method in a file StringExt.kt

fun String.removeNonAlphanumeric(s: String) = s.replace([^a-ZA-Z0-9].Regex(), "")

But Kotlin in not allowing me to use this method in a lambda:

s.split("\\s ".Regex())
.map(String::removeNonAlphanumeric)
.toList()

The error is:

Required: (TypeVariable(T)) -> TypeVariable(R)
Found: KFunction2<String,String,String>

What confuses me about this is that Kotlins Strings.kt has very similar methods and I can call them by reference without Intellij raising this kind of issue. Any advice is appreciated.

CodePudding user response：

This is because you have declared an extension function that accepts an additional parameter and should be used as s.replace("abc").

I think what you meant is the following:

fun String.removeNonAlphanumeric(): String = this.replace("[^a-ZA-Z0-9]".toRegex(), "")

This declaration doesn't have an extra parameter and uses this to refer to the String instance it is called on.

CodePudding user response：

I thing this is because a lambda is an anonymous function and dose not access to the scope of a extension file.

Check this link maybe contains some useful information: https://kotlinlang.org/docs/reference/extensions.html