What is the advantage of using `either` over `either eager` kotlinlang #arrow

Lukasz Kalnik

08/03/2022, 3:20 PM

What is the advantage of using

either

either.eager

for suspending computations? If I use

either.eager

, will it simply block the current thread?

suspend fun doSomethingLong(): Either<Error, Unit>

either.eager {
    doSomethingLong() // does it block the current thread?
}

08/03/2022, 3:20 PM

Does that even compile?

Lukasz Kalnik

08/03/2022, 3:20 PM

public final inline fun <E, A> eager(
    crossinline f: suspend EagerEffectScope<E>.() → A
): Either<E, A>

simon.vergauwen

08/03/2022, 3:23 PM

That should not compile

EagerEffectScope

@RestrictSuspension

Lukasz Kalnik

08/03/2022, 3:24 PM

It compiles at least inside of another

suspend

function, maybe that's the catch

simon.vergauwen

08/03/2022, 3:26 PM

Ah yes. It’s

inline

so it uses the

suspend

fro the outer scope.

Lukasz Kalnik

08/03/2022, 3:26 PM

That explains it.

simon.vergauwen

08/03/2022, 3:27 PM

Hmm.. It’s not compiling for me though 🤯

Where is your

suspend

suspend

eager

in your screenshot

Only the call to

bind

but that should be coming from

eager

Lukasz Kalnik

08/03/2022, 3:28 PM

So the IDE shows

bind()

as the suspend function...

simon.vergauwen

08/03/2022, 3:28 PM

Yes, but that is coming from

EagerEffectScope

so it’s allowed

delay(100)

should not be allowed

Lukasz Kalnik

08/03/2022, 3:29 PM

Makes sense, I just misinterpreted the "suspend" marker in the gutter

Thanks for the explanation!

Ok, so in this case, is there a difference if I use

either

either.eager

? I suppose not. Or is there a reason why I should use

either

, e.g. because my outer function is suspending anyway?

simon.vergauwen

08/03/2022, 3:31 PM

In this case there is no difference at all. You’re free to use both.