Hey suppose I have a Student like `data class Student(val id: Int, val name: String)` and I’m tryin...

# kotest

[André Martins]

Hey suppose I have a Student like data class Student(val id: Int, val name: String) and I’m trying to build a Arb of Student like

fun Arb.Companion.student(
    id: Arb<Int> = positiveInt(),
    name: Arb<String> = string()
): Arb<Student> = arbitrary { rs ->
    Student(
        id.next(rs),
        name.next(rs) // or name.bind() and ignore rs?
    )
}

Should I call bind or next with the current randomSource?

[Emil Kantis]

I think you can do Arb.bind(id, name, ::Student)

[André Martins]

?

[mitch]

@André Martins I'd recommend using .bind. that will make sure all edgecases from all arbs are incorporated

[André Martins]

Ok, but then when I do Arb.student().next(myRandomSource) will it pass the random source to all arbs?

[mitch]

yep that’s right. next will call the random sample and discards all edgecases

[André Martins]

ok thx

[mitch]

hence if i were you, i’d do your second approach as in

fun Arb.Companion.student(
    id: Arb<Int> = positiveInt(),
    name: Arb<String> = string()
): Arb<Student> = arbitrary { 
    Student(
        id.bind(),
        name.bind()
    )
}

[mitch]

internally that will basically do all the correct things including the propagation of random source, as well as settings for edgecases - both for id-arb and name arb, and all other composed arbs therein

[André Martins]

Basically we should only use next outside and bind for composition right?

[Emil Kantis]

My example was shorthand of the above. Arb.bind(id, name, ::Student) takes the id and name arb and binds them using the Student constructor. 🙂

[mitch]

yep that’s right. outside of the arbitrary { } scope, that’s about the only thing possible. within the builder you can compose a lot more complex arbitraries

[André Martins]

Oh ok I rather call constructor explicitly

[André Martins]

thanks guys!