Contract is not truly type safe

Hello, I wanted to leverage the ‘type safe’ contract http4k claims to provide to ensure (at compile time) that a handler for given route/method responds with correct response type. However, from the available documentation I was not able to figure out how to do that or whether that’s even possible.

Consider following example

data class City(
        val id: Long,
        val name: String,
)

fun getCity(): ContractRoute {
    val openApiSpec = "city/v1/get" meta {
        // type of the response is defined here to be City
        returning(Status.OK, Body.auto<City>().toLens() to City(id = 123, name = "Prague"))
    } bindContract Method.GET

    return openApiSpec to {
        // this is expected to fail at compile type because it does not conform to the spec above
        Response(Status.OK, "booya!")
    }
}

Can the expectation be fulfilled? If so, how?

[daviddenton]

Yep - we’re aware of this and you are of course correct. There is a fine balance between making the API comprehensible (and avoiding magic), which is obviously a little out of whack here.

… that said - there is a bit of a side project that we’ve been playing with to come up with a completely typesafe routing module which can be bound to create both server and client bindings. It’s early days, but we’re quite hopeful it might be something that has legs… 😃

[daviddenton]

There is no news on this feature request.