Hi all! Want to collect some ideas about the probl...

# server

[Alex Stelmachonak]

Hi all! Want to collect some ideas about the problem I have in Kotlin+Jackson space.

I wanted to implement something like this:

interface HttpResponseBody {
	val asString: String
	
	inline fun <reified T : Any> asInstanceOf(format: BodyFormat): T =
        when (format) {
            BodyFormat.JSON -> jacksonObjectMapper().readValue(asString)
        }
}

so I can utilize the jackson-kotlin support of reified type parameters to not pass class instance to the deserialization method and be able to use it like this

response.body.asInstanceOf<User>(BodyFormat.JSON)

But reified only works in inline functions and I can't inline the function in interface. I was looking for not ugly way to workaround that and have similar implementation in place. So far I found two ways of doing this:
1. Convert HttpResponseBody to abstract class, so inline and reified are working.
2. Convert asInstanceOf method to the extension method of the HttpResponseBody interface.
Both are working, but doesn't fit nicely with my other codebase (which I probably need to refactor), but I wanted to ask may be I am missing some other solutions?

[mitch]

Hey @Alex Stelmachonak I'm curious of what others do as well but what I usually do is to define a non-inline function in the interface, and then declare an inline extension function on the interface. Something like this:

interface HttpResponseBody {
  fun <T> instanceOf(bodyFormat: BodyFormat, clazz: Class<T>): T
}

inline fun <reified T> HttpResponseBody.instanceOf(bodyFormat: BodyFormat) = instanceOf(bodyFormat, T::class.java)

[mitch]

Oh you had tried this already in your second approach.

[Alex Stelmachonak]

Thanks! The issue here is that I can't just call method from interface from the extension function - jackson kotlin method readValue requires generic type to be reified , which is not possible.

If I just do T::class.java it kind of works, but looses the benefits of Kotlin classes additional runtime data. I.e. I can't just use data class without extra @JsonProperty annotations.

[Alex Stelmachonak]

I will put this aside for some time and will try to fix it in few days - want to have a fresh look at this

[DALDEI]

use the same type function that jackson-kotlin uses, not T::class.java use
instanceOf( bodyFormat , jacksonTypeRef<T>() )