在scala中实现泛型半群实现

Question

我试图以一种通用的方式为包括集合在内的大多数scala类型实现SemiGroup。但是当涉及到集合时，我坚持实现集合的隐式SemiGroupImplicitTypes。

例如:如果我想实现一个SemiGroup[ListT]，它需要列表中的元素类型的另一个参数，我不想单独实现SemiGroup[ListInt]，SemiGroup[ListDouble]，我想要一个隐式的实现，它将为所有类型的列表实现它。

trait Semigroup[T] extends Any {
  def combine(a: T, b: T): T
}

object SemiGroup {
  def apply[T](a: T, b: T)(implicit ev: Semigroup[T]): T = ev.combine(a,b)
}

class SemiGroupList[T] extends Semigroup[List[T]] {
  override def combine(a: List[T], b: List[T]): List[T] = a ++ b
}

class SemiGroupSeq[T] extends Semigroup[Seq[T]] {
  override def combine(a: Seq[T], b: Seq[T]): Seq[T] = a ++ b
}

class SemiGroupMap[U, V] extends Semigroup[Map[U,V]] {
  override def combine(a: Map[U, V], b: Map[U, V]): Map[U, V] = a ++ b
}

class SemiGroupNumber[@specialized (Int, Double, Float, Long) T](implicit numeric: Numeric[T]) extends Semigroup[T] {
  override def combine(a: T, b: T): T = numeric.plus(a, b)
}

object SemiGroupImplicitTypes {
  implicit object IntSemiGroup extends SemiGroupNumber[Int]
  implicit object LongSemiGroup extends SemiGroupNumber[Long]
  implicit object DoubleSemiGroup extends SemiGroupNumber[Double]
  implicit object FloatSemiGroup extends SemiGroupNumber[Float]
}


import SemiGroupImplicitTypes._
SemiGroup[Long](1,2)

Answer 1

将其设为def：

 implicit def semigroupList[T] = new SemiGroupList[T]

Answer 2

您需要实现带类型参数的defs：

object SemiGroupImplicitTypes {
    implicit object IntSemiGroup extends SemiGroupNumber[Int]
    implicit object LongSemiGroup extends SemiGroupNumber[Long]
    implicit object DoubleSemiGroup extends SemiGroupNumber[Double]
    implicit object FloatSemiGroup extends SemiGroupNumber[Float]

    implicit def listSemiGroup[T]: Semigroup[List[T]] = new SemiGroupList[T]
}

Answer 3

trait Semigroup[T] extends Any {
  def combine(a: T, b: T): T
}

object SemiGroup {
  def apply[T](a: T, b: T)(implicit ev: Semigroup[T]): T = ev.combine(a,b)
}

class SemiGroupList[T] extends Semigroup[List[T]] {
  override def combine(a: List[T], b: List[T]): List[T] = a ++ b
}

class SemiGroupSeq[T] extends Semigroup[Seq[T]] {
  override def combine(a: Seq[T], b: Seq[T]): Seq[T] = a ++ b
}

class SemiGroupMap[U, V] extends Semigroup[Map[U,V]] {
  override def combine(a: Map[U, V], b: Map[U, V]): Map[U, V] = a ++ b
}

class SemiGroupNumber[@specialized (Int, Double, Float, Long) T](implicit numeric: Numeric[T]) extends Semigroup[T] {
  override def combine(a: T, b: T): T = numeric.plus(a, b)
}

object SemiGroupImplicitTypes {
  implicit def numberSemiGroup[T](implicit numeric: Numeric[T]) = new SemiGroupNumber[T]()
  implicit def listSemiGroup[T] = new SemiGroupList[T]()
  implicit def mapSemiGroup[U,V] = new SemiGroupMap[U,V]()
  implicit def seqSemiGroup[U] = new SemiGroupSeq[U]()
}

import SemiGroupImplicitTypes._


SemiGroup[Int](1,2)
SemiGroup[List[Int]](List[Int](1,2,3), List(2,3,5))

我使用def实现的实现的修改版本。