Challenge 2: Interface with a Default Method — Solution

interface Greetable {
    val name: String
    fun customGreeting(): String
    fun greet() = println(customGreeting())
}

class FormalPerson(override val name: String) : Greetable {
    override fun customGreeting() = "Good day, I am $name."
}

class CasualPerson(override val name: String) : Greetable {
    override fun customGreeting() = "Hey, it's $name!"
}

fun main() {
    val formal: Greetable = FormalPerson("Dr. Smith")
    val casual: Greetable = CasualPerson("Jamie")

    formal.greet()
    casual.greet()
}

/*
Output:
Good day, I am Dr. Smith.
Hey, it's Jamie!

Notes:
- name and customGreeting() are abstract — every class implementing
  Greetable must supply both.
- greet() has a default body in the interface itself, so neither
  FormalPerson nor CasualPerson needs to implement it — both inherit the
  same greet() logic, which simply calls each class's own customGreeting().
- override is required on "val name" in each class because interface
  properties, like interface methods, must be explicitly overridden.
*/