The Path to Generic Endpoints using Shapeless
Maria Livia Chiorean
Me
@MariaLiviaCh
Content Atoms
- Structured data
- Reusable content
- Simultaneous updates
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Atom Workshop
- We have 10 types of atoms
- Common components
- Shared services
- Built on Scala, Play and React
Generic API Endpoint
PATCH /api/:atomType/:id/:path
val atomData = MediaAtom(
url = "gu.com",
metadata = Some(Metadata(
commentsEnabled = Some(true),
channelId = Some("happy-friday"))))
val atomData = MediaAtom(
title = "Tech time video",
metadata = Some(Metadata(
commentsEnabled = Some(true),
channelId = Some("Scala"))))
/api/media/some-id/metadata.channelId
body: "Scala"
Shapeless
- Library for generic programming in Scala
- Leverages the similarities between types
case class Employee(name: String, age: Int, manager: Boolean)
case class IceCream(name: String, numCherries: Int, inCone: Boolean)
String :: Int :: Boolean :: HNil
HList
Generic[IceCream].to(iceCream)
Generic[Employee].to(iceCream)
First approach
val atomData = MediaAtom(url = "gu.com",
metadata = Some(Metadata(
commentsEnabled = Some(true),
channelId = Some("happy-friday"))))
val mediaAtom = Atom("some-id", "media", "Scala fun", AtomData.Media(atomData))
val genericRepr = LabelledGeneric[Atom].to(mediaAtom)
// "some-id" :: "media" :: "Scala fun" :: Media(MediaAtom(...)) :: HNil
val updatedGeneric = genericRepr + (Symbol("title") ->> "Updated title"))
// "some-id" :: "media" :: "Updated title" :: Media(MediaAtom(...)) :: HNil
val updatedGeneric2 = genericRepr + (Symbol(nestedField) ->> "Updated field"))
// error: Expression scala.Symbol.apply(ScalaFiddle.this.nestedField) does
// not evaluate to a constant or a stable reference value
Atom
id: String
type: String
title: String
data: AtomData
media: MediaAtom
metadata: Metadata
url: String
comments: Boolean
channelId: String
Second approach
Convert to nested maps
Update the field in the map
Type Classes
trait Greetings[A] {
def message(creature: A): String
}
object Greetings {
implicit def humanMessage: Greetings[Human] = new Greetings[Human] {
override def message(human: Human): String = s"${human.name} says hello."
}
implicit def catMessage: Greetings[Cat] = new Greetings[Cat] {
override def message(cat: Cat): String = s"${cat.name} says meow."
}
implicit class GreetingsOps[A](creature: A) {
def greet(implicit greetings: Greetings[A]) = {
greetings.message(creature)
}
}
}
Human("Maria").greet // "Maria says hello."
Cat("Mistoffelees").greet // "Mistoffelees says meow."
Dog("Pollicle").greet // error: could not find implicit value for parameter message
Class to map
trait ToMapRec[L <: HList] {
def apply(l: L): Map[String, Any]
}
object ToMapRec {
implicit def hconsToMapRecOption[K <: Symbol, V, R <: HList, T <: HList]
(implicit
wit: Witness.Aux[K],
gen: LabelledGeneric.Aux[V, R],
tmrT: Lazy[ToMapRec[T]],
tmrH: Lazy[ToMapRec[R]]
): ToMapRec[FieldType[K, Option[V]] :: T] = ???
}
Class to map
trait ToMapRec[L <: HList] {
def apply(l: L): Map[String, Any]
}
...
implicit def hconsToMapRecOption[K <: Symbol, V, R <: HList, T <: HList]
(implicit
wit: Witness.Aux[K],
gen: LabelledGeneric.Aux[V, R],
tmrT: Lazy[ToMapRec[T]],
tmrH: Lazy[ToMapRec[R]]
): ToMapRec[FieldType[K, Option[V]] :: T] = new ToMapRec[FieldType[K, Option[V]] :: T] {
override def apply(l: FieldType[K, Option[V]] :: T): Map[String, Any] = {
tmrT.value(l.tail) + (wit.value.name -> l.head.map(elem => tmrH.value(gen.to(elem))))
}
}
...
val atomMap = atomData.toMap
val atomDataMap = Map(
"metadata" -> Some(Map(
"commentsEnabled" -> Some(false),
"channelId" -> Some("happy-friday"))),
"url" -> "gu.com")
Final approach
Summary
- New and shiny is fun.
- Shapeless book: The Type Astronaut's Guide to Shapeless
- Code: github.com/marialivia16/scrooge-shapeless-maps
Thank you.
Short - The Path to Generic Endpoints using Shapeless
By Maria Livia
Short - The Path to Generic Endpoints using Shapeless
WHC meetup
- 1,101