slices: relax the constraints to type whose underlying type is slice

Like what we done in exp/maps, exp/slices would be better to accept a
type whose underlying type is slice.

Due to golang/go#48619, constraints of quickSortOrdered and its
related functions are not changed. So cast S to []E for now.

Author: SilverRainZ

slices/slices.go

@@ -14,7 +14,7 @@ import "constraints"
 // Otherwise, the elements are compared in increasing index order, and the
 // comparison stops at the first unequal pair.
 // Floating point NaNs are not considered equal.
-func Equal[E comparable](s1, s2 []E) bool {
+func Equal[S ~[]E, E comparable](s1, s2 S) bool {
 	if len(s1) != len(s2) {
 		return false
 	}
@@ -31,7 +31,7 @@ func Equal[E comparable](s1, s2 []E) bool {
 // EqualFunc returns false. Otherwise, the elements are compared in
 // increasing index order, and the comparison stops at the first index
 // for which eq returns false.
-func EqualFunc[E1, E2 any](s1 []E1, s2 []E2, eq func(E1, E2) bool) bool {
+func EqualFunc[S1 ~[]E1, S2 ~[]E2, E1, E2 any](s1 S1, s2 S2, eq func(E1, E2) bool) bool {
 	if len(s1) != len(s2) {
 		return false
 	}

slices/sort.go

@@ -7,26 +7,28 @@ package slices
 import "constraints"
 
 // Sort sorts a slice of any ordered type in ascending order.
-func Sort[Elem constraints.Ordered](x []Elem) {
+func Sort[S ~[]E, E constraints.Ordered](x S) {
 	n := len(x)
-	quickSortOrdered(x, 0, n, maxDepth(n))
+	// Due to golang/go#48619, constraints of quickSortOrdered and its related
+	// functsions are not changed. So cast S to []E for now.
+	quickSortOrdered([]E(x), 0, n, maxDepth(n))
 }
 
 // Sort sorts the slice x in ascending order as determined by the less function.
 // This sort is not guaranteed to be stable.
-func SortFunc[Elem any](x []Elem, less func(a, b Elem) bool) {
+func SortFunc[S ~[]E, E any](x S, less func(a, b E) bool) {
 	n := len(x)
 	quickSortLessFunc(x, 0, n, maxDepth(n), less)
 }
 
 // SortStable sorts the slice x while keeping the original order of equal
 // elements, using less to compare elements.
-func SortStableFunc[Elem any](x []Elem, less func(a, b Elem) bool) {
+func SortStableFunc[S ~[]E, E any](x S, less func(a, b E) bool) {
 	stableLessFunc(x, len(x), less)
 }
 
 // IsSorted reports whether x is sorted in ascending order.
-func IsSorted[Elem constraints.Ordered](x []Elem) bool {
+func IsSorted[S ~[]E, E constraints.Ordered](x S) bool {
 	for i := len(x) - 1; i > 0; i-- {
 		if x[i] < x[i-1] {
 			return false
@@ -37,7 +39,7 @@ func IsSorted[Elem constraints.Ordered](x []Elem) bool {
 
 // IsSortedFunc reports whether x is sorted in ascending order, with less as the
 // comparison function.
-func IsSortedFunc[Elem any](x []Elem, less func(a, b Elem) bool) bool {
+func IsSortedFunc[S ~[]E, E any](x S, less func(a, b E) bool) bool {
 	for i := len(x) - 1; i > 0; i-- {
 		if less(x[i], x[i-1]) {
 			return false
@@ -51,7 +53,7 @@ func IsSortedFunc[Elem any](x []Elem, less func(a, b Elem) bool) bool {
 // which it could be inserted into the slice is returned; therefore, if the
 // intention is to find target itself a separate check for equality with the
 // element at the returned index is required.
-func BinarySearch[Elem constraints.Ordered](x []Elem, target Elem) int {
+func BinarySearch[S ~[]E, E constraints.Ordered](x S, target E) int {
 	return search(len(x), func(i int) bool { return x[i] >= target })
 }
 
@@ -63,7 +65,7 @@ func BinarySearch[Elem constraints.Ordered](x []Elem, target Elem) int {
 // the first true index. If there is no such index, BinarySearchFunc returns n.
 // (Note that the "not found" return value is not -1 as in, for instance,
 // strings.Index.) Search calls ok(i) only for i in the range [0, n).
-func BinarySearchFunc[Elem any](x []Elem, ok func(Elem) bool) int {
+func BinarySearchFunc[S ~[]E, E any](x S, ok func(E) bool) int {
 	return search(len(x), func(i int) bool { return ok(x[i]) })
 }