Can private properties or methods be declared inside extension functions in Kotlin?

In Kotlin, extension functions cannot contain their own properties or methods, as they are essentially static functions that extend the functionality of existing classes without modifying their source code.

Therefore, it is impossible to declare private properties or methods inside an extension function. An extension function can only use public or protected members of the class it is applied to and cannot store state.

Example of an extension function:

fun String.isPalindrome(): Boolean {
    return this == this.reversed()
}

Here, you cannot add a private property or method inside isPalindrome.