强制严格集合

斯卡拉 Seq 他们没有捕捉到足够的信息来决定他们是否严格。

您可以将要接受的序列列为白名单,如下所示:

import scala.language.higherKinds

// Tag for sequences that are strict.
sealed trait StrictSeq[T[_] <: Seq[_]]

object StrictSeq {
  // Evidence for the compiler that lists and vectors are strict.
  implicit object ListIsStrict   extends StrictSeq[List]
  implicit object VectorIsStrict extends StrictSeq[Vector]
}

// Restrict S to be a sequence and to have been tagged as strict.
case class Foo[S[_] <: Seq[_] : StrictSeq](xs: S[Int])

Foo(List(1, 2, 3))    // OK
Foo(Vector(1, 2, 3))  // OK
Foo(Stream(1, 2, 3))  // Compile-time error