Kotlin Programming: The Big Nerd Ranch Guide, 2nd Edition

expect and actual

So far, so good. But it would be nicer if Doubloons4Gold used currency formatting, so your output looked like this:

    Hello from Kotlin/JVM!
    The current exchange rate is $1.38 per doubloon
    How many doubloons do you want?
    50
    50.0 doubloons will cost you $69.04

You want this formatting to apply across all platforms your application supports, so it belongs in your common codebase. Create a new file in commonMain/kotlin called Currency.kt and define an extension function on Double called formatAsCurrency.

As the name suggests, this function will convert a double to an appropriately formatted string for the user’s local currency. But for now, leave the implementation as a to-do. We will explain how to implement it shortly. ...