Hello all. Can i build an entire Rest API with arrow + ktor without using OO (classes, inheritance ....

# arrow

[Rodrigo Silva]

Hello all. Can i build an entire Rest API with arrow + ktor without using OO (classes, inheritance ...)?

[pakoito]

Depends on whether ktor requires them or not. In general we don't shy away from implementing interfaces if you consider that inheritance

[pakoito]

I've shipped a 20k LOC project in PHP with only a couple of interface implementations so...it should be possible in Kotlin too

[pakoito]

with or without Arrow

[Bob Glamm]

I've shipped a 20k LOC project in PHP

Paco, you are a brave, brave man

[Rodrigo Silva]

thanks for answer @pakoito

[pakoito]

@Bob Glamm I'm cheating a little bit because it's in Hacklang...which is PHP + F# 😛

[pakoito]

@Rodrigo Silva why do you want to impose those restrictions? and I hope I answered your question. I'm unsure of the context.

[Rodrigo Silva]

@pakoito I wanted to program without using OO, only functional, like an Elixir, or Heskell, but using Kotlin.

[Satyam Agarwal]

I’ve started doing exactly that, and its been coming out really good.
Here is my stack HOCON format with config4k + arrow-kt (IO + Reader) + ktor + JUnit5 (for running every test node parallely) + Docker Test containers. Not a single test contains mocks, and the beauty is, I can write tests from repository layer til right to the routers. Super happy with just arrow-kt

[Satyam Agarwal]

To add to that I extensively use data classes to hold data and just that, and sealed classes to handle exception, each exception is a domain layer Left hand side object, and right before sending out response, I can just do IO.attempt().map { … } and in that do pattern matching to handle all types of known and unknown exceptions

[Satyam Agarwal]

aahhh…. I cannot tell you how much I love arrow

[Satyam Agarwal]

The only problem is, respond(…) method which actually sends response in ktor, can only be called with ApplicationCall instance, so I cannot make an extension function on IO to send response, and then it ends up looking like this :
IO.effect { myDomainResponse -> this.call.respond(myDomainResponse) }

which is not nice from purity point of view.

[Satyam Agarwal]

But its life

[pakoito]

@Satyam Agarwal can I please tweet about your experience? It made me so happy to hear 😄

[Satyam Agarwal]

Hahah, Sure 🙂

[Rodrigo Silva]

@Satyam Agarwal could you share your code? I really need a starting point. I recently did a series of articles about ktor + kafka. Now I would like to use Arrow to make everything functional

[Satyam Agarwal]

It’s actually company’s property so can’t do that. But I can make some dummy project and share. Just need to wait a little. Too much going on at work. But I’ve been thinking to do that anyway

[Rodrigo Silva]

that would be cool

[than_]

The only problem is, respond(…) method which actually sends response in ktor, can only be called with ApplicationCall instance, so I cannot make an extension function on IO to send response, and then it ends up looking like this :

IO.effect { myDomainResponse -> this.call.respond(myDomainResponse) }

which is not nice from purity point of view.

I've had the same problem. This can be helped with few extension functions.

inline fun <reified T : Any> <http://Route.post|Route.post>(noinline body: suspend ConcurrentSyntax<ForIO>.(call: ApplicationCall, args: T) -> Unit): Route =
    post<T>{
        IO.fx {
            body(call, it)
        }.suspendCancellable()
    }

fun ApplicationCall.respondEffect(status: HttpStatusCode, message: Any): IO<Unit> =
    IO.effect { respond(status, message) }