workbook.kt

// In Kotlin function definitions start with the keywork "fun"
// Additionally Kotlin lets you have "top level" functions that do not need to be inside a class
// "(Workbook) -> Unit" means "a function that takes a workbook and returns nothing (Unit)
fun workbook(block: (Workbook) -> Unit): Workbook {
    var wb = HSSFWorkbook()
    // Note that in Kotlin we can direcly call "block" rather than needing to call "accept" on it
    block(wb)
    return wb
}

fun tryItOut() {
    workbook({wb ->
        wb.setHidden(true)
        wb.setSelectedTab(2)
    })
    
    // In Kotlin you can drop the lambda parameters name and use the default name "it"
    workbook({
        it.setHidden(true)
        it.setSelectedTab(2)
    })

    // In Kotlin if the last parameter of a method is a lambda then you can move it outside the parenthesis 
    workbook() {
        it.setHidden(true)
        it.setSelectedTab(2)
    }

    // Also since the lambda is the only parameter we can even drop the parenthesis all together! 
    workbook {
        it.setHidden(true)
        it.setSelectedTab(2)
    }
}