doApiCallWithArg.kt

import kotlin.reflect.KFunction2 // You have to import this manually

inline fun <reified Service: RetroService, Input, Result> doApiCallWithArg(
    services: List<RetroService>,
    apiCall: KFunction2<Service, Input, Result>,
    input: Input
): Result? {
    Log.v(TAG, "Attempting to do \$apiCall on \$services with argument \$input")

    services.filterIsInstance<Service>()
        .forEach { service ->
            val result = apiCall(service, input)
            Log.i(TAG, "Returned result $result")
            return result
        }

    Log.d(TAG, "None of the services were compatible, returning null")
    return null
}

fun listGitHubReposForJacques(services: List<RetroService>): List<GitHubRepo>? {
    val username = "JacquesSmuts"
    return doApiCallWithArg(services, GitHubService::listGitHubRepos, username)    
}