scala 通用排序函数不适用于数组
scala generic sort function doesn't work with arrays
我正在尝试编写一个适用于任何序列的排序函数,returns 传递给此函数的相同序列。所以我想出了这个解决方案:
def qckSrt[U: Ordering, C <: Seq[U]](xs: C with SeqLike[U, C])
(implicit bf: CanBuildFrom[C, U, C]): C = {
val n = xs.length
val b = bf()
if (n <= 1) xs
else {
val p = xs.head
val (left, right) = xs.tail partition {
implicitly[Ordering[U]].lteq(_, p)
}
b ++= qckSrt(left)
b += p
b ++= qckSrt(right)
b.result()
}
}
所以它适用于列表、向量、数组缓冲区...但它不适用于普通数组:
scala> qckSrt(Array(1, 2, 6, 2, 5))
<console>:16: error: inferred type arguments [Int,Any] do not conform to method qckSrt's type parameter bounds [U,C <: Seq[U]]
qckSrt(Array(1, 2, 6, 2, 5))
^
<console>:16: error: type mismatch;
found : scala.collection.mutable.ArrayOps.ofInt
required: C with scala.collection.SeqLike[U,C]
qckSrt(Array(1, 2, 6, 2, 5))
^
<console>:16: error: No implicit Ordering defined for U.
qckSrt(Array(1, 2, 6, 2, 5))
有没有办法让数组也能正常工作?
您可以用隐式转换代替继承。对于数组,这将使用隐式包装转换,对于已经是 SeqLike
的类型,它将使用子类型证据 (implicitly[C[U] <:< SeqLike[U, C[U]]]
):
import scala.collection._
import scala.collection.generic.CanBuildFrom
def qckSrt[U: Ordering, C[_]](xs: C[U])(implicit
bf: CanBuildFrom[C[U], U, C[U]],
asSeq: C[U] => SeqLike[U, C[U]]
): C[U] = {
val n = xs.length
val b = bf()
if (n <= 1) xs
else {
val p = xs.head
val (left, right) = xs.tail partition {
implicitly[Ordering[U]].lteq(_, p)
}
b ++= qckSrt(left)
b += p
b ++= qckSrt(right)
b.result()
}
}
需要将 "hole" 添加到类型 C
才能在调用站点正确推断 U
。
我正在尝试编写一个适用于任何序列的排序函数,returns 传递给此函数的相同序列。所以我想出了这个解决方案:
def qckSrt[U: Ordering, C <: Seq[U]](xs: C with SeqLike[U, C])
(implicit bf: CanBuildFrom[C, U, C]): C = {
val n = xs.length
val b = bf()
if (n <= 1) xs
else {
val p = xs.head
val (left, right) = xs.tail partition {
implicitly[Ordering[U]].lteq(_, p)
}
b ++= qckSrt(left)
b += p
b ++= qckSrt(right)
b.result()
}
}
所以它适用于列表、向量、数组缓冲区...但它不适用于普通数组:
scala> qckSrt(Array(1, 2, 6, 2, 5))
<console>:16: error: inferred type arguments [Int,Any] do not conform to method qckSrt's type parameter bounds [U,C <: Seq[U]]
qckSrt(Array(1, 2, 6, 2, 5))
^
<console>:16: error: type mismatch;
found : scala.collection.mutable.ArrayOps.ofInt
required: C with scala.collection.SeqLike[U,C]
qckSrt(Array(1, 2, 6, 2, 5))
^
<console>:16: error: No implicit Ordering defined for U.
qckSrt(Array(1, 2, 6, 2, 5))
有没有办法让数组也能正常工作?
您可以用隐式转换代替继承。对于数组,这将使用隐式包装转换,对于已经是 SeqLike
的类型,它将使用子类型证据 (implicitly[C[U] <:< SeqLike[U, C[U]]]
):
import scala.collection._
import scala.collection.generic.CanBuildFrom
def qckSrt[U: Ordering, C[_]](xs: C[U])(implicit
bf: CanBuildFrom[C[U], U, C[U]],
asSeq: C[U] => SeqLike[U, C[U]]
): C[U] = {
val n = xs.length
val b = bf()
if (n <= 1) xs
else {
val p = xs.head
val (left, right) = xs.tail partition {
implicitly[Ordering[U]].lteq(_, p)
}
b ++= qckSrt(left)
b += p
b ++= qckSrt(right)
b.result()
}
}
需要将 "hole" 添加到类型 C
才能在调用站点正确推断 U
。