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This makes it easy to compact slices that contain duplicate elements by sorting and then uniqing. This is an alternative to constructing an intermediate map and then extracting elements from it. It also provides more control over equality than using a map key does. Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
66 lines
1.5 KiB
Go
66 lines
1.5 KiB
Go
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package uniq provides removal of adjacent duplicate elements in slices.
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// It is similar to the unix command uniq.
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package uniq
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import (
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"fmt"
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"reflect"
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)
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type badTypeError struct {
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typ reflect.Type
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}
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func (e badTypeError) Error() string {
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return fmt.Sprintf("uniq.ModifySlice's first argument must have type *[]T, got %v", e.typ)
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}
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// ModifySlice removes adjacent duplicate elements from the slice pointed to by sliceptr.
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// It adjusts the length of the slice appropriately and zeros the tail.
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// eq reports whether (*sliceptr)[i] and (*sliceptr)[j] are equal.
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// ModifySlice does O(len(*sliceptr)) operations.
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func ModifySlice(sliceptr interface{}, eq func(i, j int) bool) {
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rvp := reflect.ValueOf(sliceptr)
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if rvp.Type().Kind() != reflect.Ptr {
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panic(badTypeError{rvp.Type()})
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}
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rv := rvp.Elem()
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if rv.Type().Kind() != reflect.Slice {
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panic(badTypeError{rvp.Type()})
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}
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length := rv.Len()
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dst := 0
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for i := 1; i < length; i++ {
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if eq(dst, i) {
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continue
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}
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dst++
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// slice[dst] = slice[i]
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rv.Index(dst).Set(rv.Index(i))
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}
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end := dst + 1
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var zero reflect.Value
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if end < length {
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zero = reflect.Zero(rv.Type().Elem())
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}
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// for i := range slice[end:] {
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// size[i] = 0/nil/{}
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// }
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for i := end; i < length; i++ {
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// slice[i] = 0/nil/{}
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rv.Index(i).Set(zero)
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}
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// slice = slice[:end]
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if end < length {
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rv.SetLen(end)
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}
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}
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