scala - Finch: not enough arguments for method 'toService' -

i've made pretty simple rest-method using finch , finagle:

val getusers:endpoint[list[user]] = get("users") {ok(getallusers())} http.serve(":8080", getusers.toservice) 

and got error:

error:(50, 32) not enough arguments method toservice: (implicit ts: io.finch.internal.toservice[list[dal.instances.user.user]])com.twitter.finagle.service[com.twitter.finagle.http.request,com.twitter.finagle.http.response]. unspecified value parameter ts.   http.serve(":8080", getusers.toservice)                                ^ 

any idea on how fix it?

the compiler error little better in recent version of finch (0.10). if have following build config:

scalaversion := "2.11.7"  librarydependencies += "com.github.finagle" %% "finch-core" % "0.10.0" 

and setup:

import com.twitter.finagle.http import io.finch._  case class user(id: string, name: string)  def getallusers(): list[user] = list(user("111", "foo mcbar")) val getusers: endpoint[list[user]] = get("users") { ok(getallusers()) } 

then when try use toservice, following:

<console>:18: error: can convert router finagle service if result type of router 1 of following:    * response   * value of type encoderesponse instance   * coproduct made of combination of above  list[user] not satisfy requirement. may need provide encoderesponse instance list[user] (or  part of list[user]).         http.serve(":8080", getusers.toservice)                                     ^ 

the problem haven't told finch how translate instances of user type http responses. finch's encoderesponse example of type class, approach polymorphism that's used in scala (including standard library) , many other statically-typed functional programming languages.

the easiest way provide appropriate encoderesponse instances add finch's circe compatibility module build:

librarydependencies ++= seq(   "io.circe" %% "circe-generic" % "0.3.0",   "com.github.finagle" %% "finch-circe" % "0.10.0" ) 

and need following imports:

import io.finch.circe._, io.circe.generic.auto._ 

and toservice work fine:

scala> http.serve(":8080", getusers.toservice) feb 26, 2016 8:32:24 com.twitter.finagle.init$$anonfun$1 apply$mcv$sp info: finagle version 6.33.0 (rev=21d0ee8b5070b735eda5c84d7aa6fbf1ba7b1635) built @ 20160203-202859 res2: com.twitter.finagle.listeningserver = group(/0:0:0:0:0:0:0:0:8080) 

now if go http://localhost:8080/users, you'll see following:

[{"id":"111","name":"foo mcbar"}] 

this looks magic, what's happening principled. circe json library provides generic codec derivation figures out @ compile-time how represent case classes json values (see blog post here more context).

the finch cookbook great resource learning more questions this, , first section goes detail other ways provide encoderresponse instances toservice needs. if have other questions or if of above isn't clear, feel free ask either here or on gitter.