为Seq集合以泛型方式创建隐式类型类实例

Question

我正试图为以下结构编写一个通用的隐式实例：

object SmartHasher {

trait GetSmartHash[T] {
def calculateHash(value: T): Int
}

object syntax {
implicit class GetHashOps[T: GetSmartHash](itemToBeHashed: T) {
def hashItSmartway(implicit GetSmartHashInstance: GetSmartHash[T]): Int =
GetSmartHashInstance.calculateHash(itemToBeHashed)
}
}
object instances {
import syntax._

implicit def stringSmartHash: GetSmartHash[String] = (s: String) =>s.size % 10 // smart demo thing :D

}

现在我正试图定义一个通用的隐式实例，它适用于任何Vector、List或Array

其中定义了其元素的smarthash方法：

我应该用什么类型来代替Seq，因为我试着用它，但它不起作用

implicit def sequenceHash[T: GetSmartHash]: GetSmartHash[Seq[T]] =
(sequence: Seq[T]) => sequence.map(element => element.hashItSmartway).product

如果我为Vector:这样的精确集合定义它

implicit def sequenceHash[T: GetSmartHash]: GetSmartHash[Vector[T]] =
(sequence: Vector[T]) => sequence.map(element => element.hashItSmartway).product

然后它就如我所期望的那样工作了。有没有建议用通用的方式为这3个集合写这篇文章，以防止重复类似的代码3次？当做

Answer 1

尝试

object instances {
import syntax._
// stringSmartHash ...

implicit def sequenceHash[Col[X] <: Iterable[X], T: GetSmartHash]: GetSmartHash[Col[T]] =
(sequence: Col[T]) => sequence.map(element => element.hashItSmartway).product
}

测试：

import instances._, syntax._
List("aa", "bbb").hashItSmartway //6
Seq("aa", "bbb").hashItSmartway //6
Vector("aa", "bbb").hashItSmartway //6

如果您希望sequenceHash也适用于Array，请将上界替换为视图绑定

implicit def sequenceHash[Col[_], T: GetSmartHash](implicit ev: Col[T] => Iterable[T]): GetSmartHash[Col[T]] =
(sequence: Col[T]) => sequence.map(element => element.hashItSmartway).product