Kotlin Standard Library Cookbook

How to do it...

1. Declare the generateRecipientsString() function header:

fun generateRecipientsString(recipients: List<Address?>): String

2. Start by removing all the null items from the recipient parameter:

fun generateRecipientsString(recipients: List<Address?>): String =        recipients.filterNotNull()

3. Transform collection elements of the Address type to the String type elements corresponding to the Address.emailAddress property:

fun generateRecipientsString(recipients: List<Address?>): String =        recipients.filterNotNull()                .map { it.emailAddress }

4. Apply the joinToString() function in order to merge collection elements into the string:

fun generateRecipientsString(recipients: List<Address?>): String =        recipients.filterNotNull()                .map { it ...