tailscale/util/uniq/slice.go

66 lines
1.5 KiB
Go

// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package uniq provides removal of adjacent duplicate elements in slices.
// 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 interface{}, 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()
dst := 0
for i := 1; i < length; i++ {
if eq(dst, i) {
continue
}
dst++
// slice[dst] = slice[i]
rv.Index(dst).Set(rv.Index(i))
}
end := dst + 1
var zero reflect.Value
if end < length {
zero = reflect.Zero(rv.Type().Elem())
}
// 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)
}
}