util/uniq: use generics instead of reflect (#5491)

This takes 75% less time per operation per some benchmarks on my mac.

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>

util/uniq/slice.go

@@ -6,60 +6,30 @@
 // It is similar to the unix command uniq.
 package uniq
 
-import (
-	"fmt"
-	"reflect"
-)
-
-type badTypeError struct {
-	typ reflect.Type
-}
-
-func (e badTypeError) Error() string {
-	return fmt.Sprintf("uniq.ModifySlice's first argument must have type *[]T, got %v", e.typ)
-}
-
-// ModifySlice removes adjacent duplicate elements from the slice pointed to by sliceptr.
-// It adjusts the length of the slice appropriately and zeros the tail.
-// eq reports whether (*sliceptr)[i] and (*sliceptr)[j] are equal.
-// ModifySlice does O(len(*sliceptr)) operations.
-func ModifySlice(sliceptr any, eq func(i, j int) bool) {
-	rvp := reflect.ValueOf(sliceptr)
-	if rvp.Type().Kind() != reflect.Ptr {
-		panic(badTypeError{rvp.Type()})
-	}
-	rv := rvp.Elem()
-	if rv.Type().Kind() != reflect.Slice {
-		panic(badTypeError{rvp.Type()})
-	}
-
-	length := rv.Len()
+// ModifySlice removes adjacent duplicate elements from the given slice. It
+// adjusts the length of the slice appropriately and zeros the tail.
+//
+// ModifySlice does O(len(*slice)) operations.
+func ModifySlice[E comparable](slice *[]E) {
+	// Remove duplicates
 	dst := 0
-	for i := 1; i < length; i++ {
-		if eq(dst, i) {
+	for i := 1; i < len(*slice); i++ {
+		if (*slice)[i] == (*slice)[dst] {
 			continue
 		}
 		dst++
-		// slice[dst] = slice[i]
-		rv.Index(dst).Set(rv.Index(i))
+		(*slice)[dst] = (*slice)[i]
 	}
 
+	// Zero out the elements we removed at the end of the slice
 	end := dst + 1
-	var zero reflect.Value
-	if end < length {
-		zero = reflect.Zero(rv.Type().Elem())
+	var zero E
+	for i := end; i < len(*slice); i++ {
+		(*slice)[i] = zero
 	}
 
-	// for i := range slice[end:] {
-	//   size[i] = 0/nil/{}
-	// }
-	for i := end; i < length; i++ {
-		// slice[i] = 0/nil/{}
-		rv.Index(i).Set(zero)
-	}
-
-	// slice = slice[:end]
-	if end < length {
-		rv.SetLen(end)
+	// Truncate the slice
+	if end < len(*slice) {
+		*slice = (*slice)[:end]
 	}
 }