Kotlin Standard Library Cookbook

How to do it...

1. Declare a new interface called EmailValidator:

interface EmailValidator {}

2. Add a string property responsible for holding the current text input:

interface EmailValidator {    var input: String}

3. Add the isEmailValid() function to the interface:

interface EmailValidator {    var input: String    fun isEmailValid(): Boolean = input.contains("@")}

4. Add the getUserLogin() function:

interface EmailValidator {    var input: String    fun isEmailValid(): Boolean = input.contains("@")    fun getUserLogin(): String =        if (isEmailValid()) {            input.substringBefore("@")        } else {            ""        }}