Shapeless in the real world: An introduction to generic programming

Shapeless is a powerful Scala library used behind many others, such as Circe or Doobie. This talk will show you how shapeless works, using it to solve a real problem.

Transcript

1. Juliano Alves
   @vonjuliano
   juliano-alves.com
   Shapeless in the real world:
   An introduction to generic
   programming.
   

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2. Who am I?
   ● Software Engineer,
   Searcher of perfect modularization,
   Lover of Functional Languages
   ● The cool ones
   Scala, Clojure, Elixir
   ● The "vintage" ones
   Java, C#, Python, Ruby
   @vonjuliano
   juliano-alves.com
   

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3. https://getquill.io
   

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5. https://github.com/juliano/pdt-client
   

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6. // ZIO Service
   object HttpClient {
   type HttpClient = Has[Service]
   trait Service {
   protected final val rootUrl =
   "http://www.transparencia.gov.br/api-de-dados/"
   def get[T](uri: String, parameters: Map[String, String])
   (implicit d: Decoder[T]): Task[T]
   }
   

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7. // ZIO Service
   // Helpers
   def get[T](resource: String,
   parameters: Map[String, String] = Map())
   (implicit d: Decoder[T]): RIO[HttpClient, List[T]] =
   RIO.accessM[HttpClient](
   _.get.get[List[T]](resource, parameters))
   def get[T](resource: String, id: Long)
   (implicit d: Decoder[T]): RIO[HttpClient, T] =
   RIO.accessM[HttpClient](
   _.get.get[T](s"$resource/$id", Map()))
   

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8. // Http4s Implementation
   private[client] final case class Http4s(client: Client[Task])
   extends HttpClient.Service with Http4sClientDsl[Task] {
   def get[T](resource: String,
   parameters: Map[String, String])
   (implicit d: Decoder[T]): Task[T] = {
   val uri = Uri(path = rootUrl + resource)
   .withQueryParams(parameters)
   client
   .expect[T](uri.toString())
   .foldM(IO.fail(_), ZIO.succeed(_))
   }
   }
   

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9. // ZIO Service
   object HttpClient {
   // …
   def http4s: URLayer[Has[Client[Task]], Has[Service]] =
   ZLayer.fromService[Client[Task], Service] {
   http4sClient: Client[Task] => Http4s(http4sClient)
   }
   }
   Module Pattern
   

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10. https://zio.dev/docs/howto/howto_use_layers
    

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11. What is the problem?
    

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12. // ZIO Service
    object HttpClient {
    type HttpClient = Has[Service]
    trait Service {
    protected final val rootUrl =
    "http://www.transparencia.gov.br/api-de-dados/"
    def get[T](uri: String, parameters: Map[String, String])
    (implicit d: Decoder[T]): Task[T]
    }
    // Algum cliente
    def siafi(request: OrgaoRequest):
    RIO[HttpClient, List[OrgaoSiafi]] =
    get[OrgaoSiafi]("orgaos-siafi", ???)
    

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13. // domain.scala
    case class OrgaoRequest(codigo: Option[String],
    descricao: Option[String],
    pagina: Int = 1)
    case class OrgaoSiafi(codigo: String,
    codigoDescricaoFormatado: String, descricao: String)
    case class OrgaoSiape(codigo: String,
    codigoDescricaoFormatado: String, descricao: String)
    

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14. // domain.scala
    case class OrgaoRequest(codigo: Option[String],
    descricao: Option[String],
    pagina: Int = 1) {
    def toMap: Map[String, String] = ???
    }
    case class OrgaoSiafi(codigo: String,
    codigoDescricaoFormatado: String, descricao: String)
    case class OrgaoSiape(codigo: String,
    codigoDescricaoFormatado: String, descricao: String)
    

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16. // domain.scala
    case class OrgaoRequest(codigo: Option[String],
    descricao: Option[String],
    pagina: Int = 1) {
    def toMap: Map[String, String] =
    Map("codigo" -> "1337",
    "descricao" -> "Orgão Federal da Carreta Furacão",
    "pagina" -> "1")
    }
    

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18. Show me the code
    

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19. // implicits.scala
    package object implicits {
    implicit class HttpRequestOps[A <: Product](val a: A) {
    def parameters(implicit toMap: ToMap.Aux[A, Symbol, Any]):
    Map[String, String] =
    a.toMap[Symbol, Any]
    .filter {
    case (_, v: Option[Any]) => v.isDefined
    case (_, v) => v != null
    }
    .map {
    case (k, v: Option[Any]) => k.name -> v.get.toString
    case (k, v) => k.name -> v.toString
    }
    }
    }
    

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20. // ZIO Service
    object HttpClient {
    type HttpClient = Has[Service]
    trait Service {
    protected final val rootUrl =
    "http://www.transparencia.gov.br/api-de-dados/"
    def get[T](uri: String, parameters: Map[String, String])
    (implicit d: Decoder[T]): Task[T]
    }
    

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21. // domain.scala
    case class OrgaoRequest(codigo: Option[String],
    descricao: Option[String],
    pagina: Int = 1) {
    def toMap: Map[String, String] = ???
    }
    

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22. object Orgaos {
    def siafi(request: OrgaoRequest):
    RIO[HttpClient, List[OrgaoSiafi]] =
    get[OrgaoSiafi]("orgaos-siafi", ???)
    }
    object CEISs {
    def by(request: CEISRequest):
    RIO[HttpClient, List[CEIS]] =
    get[CEIS]("ceis", ???)
    }
    

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23. import pdt.implicits.HttpRequestOps
    object Orgaos {
    def siafi(request: OrgaoRequest):
    RIO[HttpClient, List[OrgaoSiafi]] =
    get[OrgaoSiafi]("orgaos-siafi",
    HttpRequestOps(request).parameters)
    }
    object CEISs {
    def by(request: CEISRequest):
    RIO[HttpClient, List[CEIS]] =
    get[CEIS]("ceis", HttpRequestOps(request).parameters)
    }
    

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24. More about shapeless
    ● https://juliano-alves.com/2020/04/06/shapeless-a-real-world-use-case/
    The post which inspired this talk
    ● https://underscore.io/books/shapeless-guide/
    The Type Astronaut's guide to shapeless
    

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25. Conclusion
    

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26. Questions?
    

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27. Juliano Alves
    @vonjuliano
    juliano-alves.com
    Shapeless in the real world:
    An introduction to generic
    programming.
    Thank you!
    

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