Another Kotlin string pitfalls

add-to-string-pitfall.md

Don't write an extension method that implement the plus operator with String arguments. If you forget to import it, the code will compile, but use string append instead.

public final class String {
  ... public final operator fun plus(other: kotlin.Any?): kotlin.String { /* compiled code */ }
}

So, always write a conversion function from String to your own type, then implement + on that type.