androidstringkotlinmethodsextending

Kotlin - Issue Extending Kotlin String Class

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.

Solution

  • 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.