package com.classLesson sealed class Person { ...

# announcements

[Udit003]

package com.classLesson


sealed class Person {

// why compiler is complaining here
class Men : Person()

class Women : Person()

abstract fun Sexuality() : String

}

class Men : Person() {
override fun Sexuality(): String {
return "M"
}
}

class Women : Person() {
override fun Sexuality(): String {
return "F"
}
}

// compiler should complain for this
class Animal : Person() {
override fun Sexuality(): String {
return "shouldn't be allowed"
}
}

fun main(args: Array<String>) {
var a: Person = Animal()
when (a) {
is Men -> println("Men")
is Animal -> println("Animal")
}
}
@

[Andreas Sinz]

Please surround your code with 3 backticks (`)

[Andreas Sinz]

1: Compiler complains about Men, because you have an abstract fun Sexuality() that isn't implemented inside the class,
2: Why should the compiler complain about Animal?

[Udit003]

Compiler should complain about Animal because I am limiting my possible derived classes to be Men , Women only

[Udit003]

That's the whole point of sealed class as per my understanding

[Andreas Sinz]

Kotlin allows you to define subclasses either inside the sealed class or in the same file

[Andreas Sinz]

You cannot inherit from Person outside of the file where it is declared

[Udit003]

Yeah so , I am defining my subclasses in the same file

[Andreas Sinz]

And by the way, you are actually declaring the Men-class twice, first inside Person and a second time beneath it

[Andreas Sinz]

thats not needed, you can either declare the class inside or beneath it

[Udit003]

So , you mean all the subclasses defined for a sealed abstract class inside the same file are valid . But they cannot be defined outside the file. Hence it does not Matter if I define my subclasses as "nested" inside the sealed class or as a top level class in the same file.

[Andreas Sinz]

exactly

[Andreas Sinz]

That way the compiler can guarantee, that when-expressions are always exhaustive

[Udit003]

Thank you so much , understood sealed classes , seems really useful and powerful