在 Scala 中为元组编写类型类 [英] Composing typeclasses for tuples in Scala
本文介绍了在 Scala 中为元组编写类型类的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我正在寻找抽象来组合类型类并避免样板代码:
I am looking for abstraction to compose typeclasses and avoid boilerplate code:
sealed trait MyTypeClass[T]{
def add(t:T, mystuff:Something)
}
object MyTypeClass {
implicit def tupled[A,B](implicit adder1: MyTypeClass [A],adder2: MyTypeClass [B]): MyTypeClass [(A,B)] = new MyTypeClass [(A, B)] {
override def add(t: (A, B), mystuff: Something): Unit = {
val (a,b) = t
adder1 add a
adder2 add b
}
}
}
有无样板的方法吗?也许是无形的?
Is there a boilerplate free approach ? Maybe in shapeless ?
推荐答案
是的,Shapeless 可以在这里帮助您,它的 TypeClass
类型类:
Yep, Shapeless can help you here, with its TypeClass
type class:
trait Something
sealed trait MyTypeClass[A] { def add(a: A, mystuff: Something) }
import shapeless._
implicit object MyTypeClassTypeClass extends ProductTypeClass[MyTypeClass] {
def product[H, T <: HList](htc: MyTypeClass[H], ttc: MyTypeClass[T]) =
new MyTypeClass[H :: T] {
def add(a: H :: T, myStuff: Something): Unit = {
htc.add(a.head, myStuff)
ttc.add(a.tail, myStuff)
}
}
def emptyProduct = new MyTypeClass[HNil] {
def add(a: HNil, mystuff: Something): Unit = ()
}
def project[F, G](instance: => MyTypeClass[G], to: F => G, from: G => F) =
new MyTypeClass[F] {
def add(a: F, myStuff: Something): Unit = {
instance.add(to(a), myStuff)
}
}
}
object MyTypeClassHelper extends ProductTypeClassCompanion[MyTypeClass]
然后:
scala> implicit object IntMyTypeClass extends MyTypeClass[Int] {
| def add(a: Int, myStuff: Something): Unit = {
| println(s"Adding $a")
| }
| }
defined module IntMyTypeClass
scala> import MyTypeClassHelper.auto._
import MyTypeClassHelper.auto._
scala> implicitly[MyTypeClass[(Int, Int)]]
res0: MyTypeClass[(Int, Int)] = MyTypeClassTypeClass$$anon$3@18e713e0
scala> implicitly[MyTypeClass[(Int, Int, Int)]]
res1: MyTypeClass[(Int, Int, Int)] = MyTypeClassTypeClass$$anon$3@53c29556
请参阅我的博文 此处其他讨论.
See my blog post here for some additional discussion.
这篇关于在 Scala 中为元组编写类型类的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!
查看全文