How to "prepend" a Char to a String in Kotlin

Question

How in Kotlin can I prepend a Char to a String?

e.g.

fun main(args: Array<String>) {
  val char = 'H'
  val string = "ello World"
  val appendingWorks = string + char //but not what I want...
  //val prependingFails = char + string //no .plus(str:String) version
  val prependingWorkaround1 = char.toString() + string
  val prependingWorkaround2 = "" + char + string
  val prependingWorkaround3 = String(charArray(char)) + string

}

When trying to call + (e.g. plus) on Char, there is no version that accepts a String on the right, so therefore 'H' + "ello World" doesn't compile

The first workaround might be good enough but it's a regression for me from what works in Java: String test = 'H' + "ello World"; (compiles fine...)

I also don't like the last workaround, at least in the java.lang.String I have a constructor that accepts a single char, or I can use java.lang.Character.toString(char c). Is there an elegant way in Kotlin to do so?

Was this discussed before (adding a plus(str:String) overload to the Char object?)

Solution 1

What about using string templates, like this:

val prepended = "$char$string"

Solution 2

As of kotlin 1.5, there is an extension plus operator function defined on Char, which can be used to concatenate a Char with given String. So you can do

val char = 'H'
val string = "ello World"

// Use the function call syntax
val result1 = char.plus(string)

// or use the operator syntax
val result2 = char + string

Comments

[Andrey Breslav]

Your second workaround looks rather good. The option with string templates suggested in the answers is equivalent and rather concise too. Nevertheless, we should consider adding Char.plus(String) to the standard library. I filed a request about it: youtrack.jetbrains.com/issue/KT-4371. Thanks for the report

[Eran Medan]

@AndreyBreslav this is great, I think Char.plus(String) will simply be more consistent with Java and Scala behavior, thanks for listening, Kotlin is getting to be my favorite Scala alternative :)

[Mitchell Tracy]

This language makes me so happy.

[Caesar]

With the plus operator the warning "Do not concatenate text displayed with setText. Use resource string with placeholders." is not shown!