lib/slicesutil: add helper functions for setting slice length and extending its capacity

The added helper functions - SetLength() and ExtendCapacity() - replace error-prone code with simple function calls.

app/vminsert/common/insert_ctx.go

@@ -9,6 +9,7 @@ import (
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/bytesutil"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/httpserver"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/prompb"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/storage"
 )
 
@@ -37,12 +38,9 @@ func (ctx *InsertCtx) Reset(rowsLen int) {
 	for i := range mrs {
 		cleanMetricRow(&mrs[i])
 	}
+	mrs = slicesutil.SetLength(mrs, rowsLen)
 	ctx.mrs = mrs[:0]
 
-	if n := rowsLen - cap(ctx.mrs); n > 0 {
-		ctx.mrs = append(ctx.mrs[:cap(ctx.mrs)], make([]storage.MetricRow, n)...)
-	}
-	ctx.mrs = ctx.mrs[:0]
 	ctx.metricNamesBuf = ctx.metricNamesBuf[:0]
 	ctx.relabelCtx.Reset()
 	ctx.streamAggrCtx.Reset()

app/vmselect/promql/rollup_result_cache.go

@@ -16,6 +16,7 @@ import (
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/memory"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/querytracer"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/storage"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/stringsutil"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/workingsetcache"
@@ -736,10 +737,7 @@ func (mi *rollupResultCacheMetainfo) Unmarshal(src []byte) error {
 	}
 	entriesLen := int(encoding.UnmarshalUint32(src))
 	src = src[4:]
-	if n := entriesLen - cap(mi.entries); n > 0 {
+	mi.entries = slicesutil.SetLength(mi.entries, entriesLen)
-		mi.entries = append(mi.entries[:cap(mi.entries)], make([]rollupResultCacheMetainfoEntry, n)...)
-	}
-	mi.entries = mi.entries[:entriesLen]
 	for i := 0; i < entriesLen; i++ {
 		tail, err := mi.entries[i].Unmarshal(src)
 		if err != nil {

app/vmselect/promql/timeseries.go

@@ -10,6 +10,7 @@ import (
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/bytesutil"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/encoding"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/storage"
 )
 
@@ -246,10 +247,7 @@ func unmarshalMetricNameFast(mn *storage.MetricName, src []byte) ([]byte, error)
 	}
 	tagsLen := encoding.UnmarshalUint16(src)
 	src = src[2:]
-	if n := int(tagsLen) - cap(mn.Tags); n > 0 {
+	mn.Tags = slicesutil.SetLength(mn.Tags, int(tagsLen))
-		mn.Tags = append(mn.Tags[:cap(mn.Tags)], make([]storage.Tag, n)...)
-	}
-	mn.Tags = mn.Tags[:tagsLen]
 	for i := range mn.Tags {
 		tail, key, err := unmarshalBytesFast(src)
 		if err != nil {

lib/bytesutil/bytebuffer.go

@@ -8,6 +8,7 @@ import (
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/filestream"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/fs"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 )
 
 var (
@@ -64,8 +65,7 @@ func (bb *ByteBuffer) ReadFrom(r io.Reader) (int64, error) {
 	offset := bLen
 	for {
 		if free := len(b) - offset; free < offset {
-			n := len(b)
+			b = slicesutil.SetLength(b, 2*len(b))
-			b = append(b, make([]byte, n)...)
 		}
 		n, err := r.Read(b[offset:])
 		offset += n

lib/decimal/decimal.go

@@ -5,6 +5,7 @@ import (
 	"sync"
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/fastnum"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 )
 
 // CalibrateScale calibrates a and b with the corresponding exponents ae, be
@@ -81,29 +82,17 @@ var decimalMultipliers = []int64{1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e
 // ExtendFloat64sCapacity extends dst capacity to hold additionalItems
 // and returns the extended dst.
 func ExtendFloat64sCapacity(dst []float64, additionalItems int) []float64 {
-	dstLen := len(dst)
+	return slicesutil.ExtendCapacity(dst, additionalItems)
-	if n := dstLen + additionalItems - cap(dst); n > 0 {
-		dst = append(dst[:cap(dst)], make([]float64, n)...)
-	}
-	return dst[:dstLen]
 }
 
 // ExtendInt64sCapacity extends dst capacity to hold additionalItems
 // and returns the extended dst.
 func ExtendInt64sCapacity(dst []int64, additionalItems int) []int64 {
-	dstLen := len(dst)
+	return slicesutil.ExtendCapacity(dst, additionalItems)
-	if n := dstLen + additionalItems - cap(dst); n > 0 {
-		dst = append(dst[:cap(dst)], make([]int64, n)...)
-	}
-	return dst[:dstLen]
 }
 
 func extendInt16sCapacity(dst []int16, additionalItems int) []int16 {
-	dstLen := len(dst)
+	return slicesutil.ExtendCapacity(dst, additionalItems)
-	if n := dstLen + additionalItems - cap(dst); n > 0 {
-		dst = append(dst[:cap(dst)], make([]int16, n)...)
-	}
-	return dst[:dstLen]
 }
 
 // AppendDecimalToFloat converts each item in va to f=v*10^e, appends it

lib/encoding/int.go

@@ -4,6 +4,8 @@ import (
 	"encoding/binary"
 	"fmt"
 	"sync"
+
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 )
 
 // MarshalUint16 appends marshaled v to dst and returns the result.
@@ -490,10 +492,7 @@ func GetInt64s(size int) *Int64s {
 		}
 	}
 	is := v.(*Int64s)
-	if n := size - cap(is.A); n > 0 {
+	is.A = slicesutil.SetLength(is.A, size)
-		is.A = append(is.A[:cap(is.A)], make([]int64, n)...)
-	}
-	is.A = is.A[:size]
 	return is
 }
 
@@ -519,10 +518,7 @@ func GetUint64s(size int) *Uint64s {
 		}
 	}
 	is := v.(*Uint64s)
-	if n := size - cap(is.A); n > 0 {
+	is.A = slicesutil.SetLength(is.A, size)
-		is.A = append(is.A[:cap(is.A)], make([]uint64, n)...)
-	}
-	is.A = is.A[:size]
 	return is
 }
 
@@ -548,10 +544,7 @@ func GetUint32s(size int) *Uint32s {
 		}
 	}
 	is := v.(*Uint32s)
-	if n := size - cap(is.A); n > 0 {
+	is.A = slicesutil.SetLength(is.A, size)
-		is.A = append(is.A[:cap(is.A)], make([]uint32, n)...)
-	}
-	is.A = is.A[:size]
 	return is
 }
 

lib/leveledbytebufferpool/pool_test.go

@@ -4,6 +4,8 @@ import (
 	"fmt"
 	"testing"
 	"time"
+
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 )
 
 func TestGetPutConcurrent(t *testing.T) {
@@ -19,7 +21,7 @@ func TestGetPutConcurrent(t *testing.T) {
 				if capacity < 0 {
 					capacity = 0
 				}
-				bb.B = append(bb.B, make([]byte, capacity)...)
+				bb.B = slicesutil.SetLength(bb.B, len(bb.B)+capacity)
 				Put(bb)
 			}
 			doneCh <- struct{}{}

lib/logstorage/indexdb.go

@@ -14,6 +14,7 @@ import (
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/mergeset"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/regexutil"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 )
 
 const (
@@ -853,13 +854,9 @@ func (sp *tagToStreamIDsRowParser) ParseStreamIDs() {
 	}
 	tail := sp.tail
 	n := len(tail) / 16
-	streamIDs := sp.StreamIDs[:0]
+	sp.StreamIDs = slicesutil.SetLength(sp.StreamIDs, n)
-	if n <= cap(streamIDs) {
+	streamIDs := sp.StreamIDs
-		streamIDs = streamIDs[:n]
+	_ = streamIDs[n-1]
-	} else {
-		streamIDs = append(streamIDs[:cap(streamIDs)], make([]u128, n-cap(streamIDs))...)
-	}
-	sp.StreamIDs = streamIDs
 	for i := 0; i < n; i++ {
 		var err error
 		tail, err = streamIDs[i].unmarshal(tail)

lib/mergeset/block_header.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/encoding"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 )
 
 type blockHeader struct {
@@ -160,10 +161,7 @@ func unmarshalBlockHeadersNoCopy(dst []blockHeader, src []byte, blockHeadersCoun
 		logger.Panicf("BUG: blockHeadersCount must be greater than 0; got %d", blockHeadersCount)
 	}
 	dstLen := len(dst)
-	if n := dstLen + blockHeadersCount - cap(dst); n > 0 {
+	dst = slicesutil.SetLength(dst, dstLen+blockHeadersCount)
-		dst = append(dst[:cap(dst)], make([]blockHeader, n)...)
-	}
-	dst = dst[:dstLen+blockHeadersCount]
 	for i := 0; i < blockHeadersCount; i++ {
 		tail, err := dst[dstLen+i].UnmarshalNoCopy(src)
 		if err != nil {

lib/mergeset/encoding.go

@@ -12,6 +12,7 @@ import (
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/bytesutil"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/encoding"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 )
 
 // Item represents a single item for storing in a mergeset.
@@ -412,10 +413,7 @@ func (ib *inmemoryBlock) UnmarshalData(sb *storageBlock, firstItem, commonPrefix
 	// since the data isn't going to be resized after unmarshaling.
 	// This may save memory for caching the unmarshaled block.
 	data := bytesutil.ResizeNoCopyNoOverallocate(ib.data, dataLen)
-	if n := int(itemsCount) - cap(ib.items); n > 0 {
+	ib.items = slicesutil.SetLength(ib.items, int(itemsCount))
-		ib.items = append(ib.items[:cap(ib.items)], make([]Item, n)...)
-	}
-	ib.items = ib.items[:itemsCount]
 	data = append(data[:0], firstItem...)
 	items := ib.items
 	items[0] = Item{
@@ -554,10 +552,7 @@ func getLensBuffer(n int) *lensBuffer {
 		v = &lensBuffer{}
 	}
 	lb := v.(*lensBuffer)
-	if nn := n - cap(lb.lens); nn > 0 {
+	lb.lens = slicesutil.SetLength(lb.lens, n)
-		lb.lens = append(lb.lens[:cap(lb.lens)], make([]uint64, nn)...)
-	}
-	lb.lens = lb.lens[:n]
 	return lb
 }
 

lib/mergeset/table_search.go

@@ -7,6 +7,7 @@ import (
 	"io"
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 )
 
 // TableSearch is a reusable cursor used for searching in the Table.
@@ -71,10 +72,7 @@ func (ts *TableSearch) Init(tb *Table) {
 	ts.pws = ts.tb.getParts(ts.pws[:0])
 
 	// Initialize the psPool.
-	if n := len(ts.pws) - cap(ts.psPool); n > 0 {
+	ts.psPool = slicesutil.SetLength(ts.psPool, len(ts.pws))
-		ts.psPool = append(ts.psPool[:cap(ts.psPool)], make([]partSearch, n)...)
-	}
-	ts.psPool = ts.psPool[:len(ts.pws)]
 	for i, pw := range ts.pws {
 		ts.psPool[i].Init(pw.p)
 	}

lib/prompbmarshal/util.go

@@ -2,16 +2,15 @@ package prompbmarshal
 
 import (
 	"fmt"
+
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 )
 
 // MarshalProtobuf marshals wr to dst and returns the result.
 func (wr *WriteRequest) MarshalProtobuf(dst []byte) []byte {
 	size := wr.Size()
 	dstLen := len(dst)
-	if n := size - (cap(dst) - dstLen); n > 0 {
+	dst = slicesutil.SetLength(dst, dstLen+size)
-		dst = append(dst[:cap(dst)], make([]byte, n)...)
-	}
-	dst = dst[:dstLen+size]
 	n, err := wr.MarshalToSizedBuffer(dst[dstLen:])
 	if err != nil {
 		panic(fmt.Errorf("BUG: unexpected error when marshaling WriteRequest: %w", err))

lib/slicesutil/slicesutil.go

@@ -0,0 +1,23 @@
+package slicesutil
+
+// ExtendCapacity returns a with the capacity extended to len(a)+itemsToAdd.
+//
+// It may allocate new slice if cap(a) is smaller than len(a)+itemsToAdd.
+func ExtendCapacity[T any](a []T, itemsToAdd int) []T {
+	aLen := len(a)
+	if n := aLen + itemsToAdd - cap(a); n > 0 {
+		a = append(a[:cap(a)], make([]T, n)...)
+		return a[:aLen]
+	}
+	return a
+}
+
+// SetLength sets len(a) to newLen and returns the result.
+//
+// It may allocate new slice if cap(a) is smaller than newLen.
+func SetLength[T any](a []T, newLen int) []T {
+	if n := newLen - cap(a); n > 0 {
+		a = append(a[:cap(a)], make([]T, n)...)
+	}
+	return a[:newLen]
+}

lib/storage/block_header.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/encoding"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 )
 
 // blockHeader is a header for a time series block.
@@ -252,10 +253,7 @@ func unmarshalBlockHeaders(dst []blockHeader, src []byte, blockHeadersCount int)
 		logger.Panicf("BUG: blockHeadersCount must be greater than zero; got %d", blockHeadersCount)
 	}
 	dstLen := len(dst)
-	if n := dstLen + blockHeadersCount - cap(dst); n > 0 {
+	dst = slicesutil.ExtendCapacity(dst, blockHeadersCount)
-		dst = append(dst[:cap(dst)], make([]blockHeader, n)...)
-		dst = dst[:dstLen]
-	}
 	var bh blockHeader
 	for len(src) > 0 {
 		tmp, err := bh.Unmarshal(src)

lib/storage/index_db.go

@@ -22,6 +22,7 @@ import (
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/memory"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/mergeset"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/querytracer"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/uint64set"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/workingsetcache"
 	"github.com/VictoriaMetrics/fastcache"
@@ -3153,13 +3154,8 @@ func (mp *tagToMetricIDsRowParser) ParseMetricIDs() {
 		return
 	}
 	tail := mp.tail
-	mp.MetricIDs = mp.MetricIDs[:0]
 	n := len(tail) / 8
-	if n <= cap(mp.MetricIDs) {
+	mp.MetricIDs = slicesutil.SetLength(mp.MetricIDs, n)
-		mp.MetricIDs = mp.MetricIDs[:n]
-	} else {
-		mp.MetricIDs = append(mp.MetricIDs[:cap(mp.MetricIDs)], make([]uint64, n-cap(mp.MetricIDs))...)
-	}
 	metricIDs := mp.MetricIDs
 	_ = metricIDs[n-1]
 	for i := 0; i < n; i++ {

lib/storage/metric_name.go

@@ -15,6 +15,7 @@ import (
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/encoding"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/prompb"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 )
 
 const (
@@ -702,10 +703,8 @@ func (mn *MetricName) sortTags() {
 	}
 
 	cts := getCanonicalTags()
-	if n := len(mn.Tags) - cap(cts.tags); n > 0 {
+	cts.tags = slicesutil.SetLength(cts.tags, len(mn.Tags))
-		cts.tags = append(cts.tags[:cap(cts.tags)], make([]canonicalTag, n)...)
+	dst := cts.tags
-	}
-	dst := cts.tags[:len(mn.Tags)]
 	for i := range mn.Tags {
 		tag := &mn.Tags[i]
 		ct := &dst[i]
@@ -775,10 +774,7 @@ func (ts *canonicalTagsSort) Swap(i, j int) {
 
 func copyTags(dst, src []Tag) []Tag {
 	dstLen := len(dst)
-	if n := dstLen + len(src) - cap(dst); n > 0 {
+	dst = slicesutil.SetLength(dst, dstLen+len(src))
-		dst = append(dst[:cap(dst)], make([]Tag, n)...)
-	}
-	dst = dst[:dstLen+len(src)]
 	for i := range src {
 		dst[dstLen+i].copyFrom(&src[i])
 	}

lib/storage/partition_search.go

@@ -6,6 +6,7 @@ import (
 	"io"
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 )
 
 // partitionSearch represents a search in the partition.
@@ -83,10 +84,7 @@ func (pts *partitionSearch) Init(pt *partition, tsids []TSID, tr TimeRange) {
 	pts.pws = pt.GetParts(pts.pws[:0], true)
 
 	// Initialize psPool.
-	if n := len(pts.pws) - cap(pts.psPool); n > 0 {
+	pts.psPool = slicesutil.SetLength(pts.psPool, len(pts.pws))
-		pts.psPool = append(pts.psPool[:cap(pts.psPool)], make([]partSearch, n)...)
-	}
-	pts.psPool = pts.psPool[:len(pts.pws)]
 	for i, pw := range pts.pws {
 		pts.psPool[i].Init(pw.p, tsids, tr)
 	}

lib/storage/search.go

@@ -10,6 +10,7 @@ import (
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/fasttime"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/querytracer"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/stringsutil"
 )
 
@@ -413,10 +414,7 @@ func (sq *SearchQuery) Unmarshal(src []byte) ([]byte, error) {
 	if err != nil {
 		return src, fmt.Errorf("cannot unmarshal the count of TagFilterss: %w", err)
 	}
-	if n := int(tfssCount) - cap(sq.TagFilterss); n > 0 {
+	sq.TagFilterss = slicesutil.SetLength(sq.TagFilterss, int(tfssCount))
-		sq.TagFilterss = append(sq.TagFilterss[:cap(sq.TagFilterss)], make([][]TagFilter, n)...)
-	}
-	sq.TagFilterss = sq.TagFilterss[:tfssCount]
 	src = tail
 
 	for i := 0; i < int(tfssCount); i++ {
@@ -427,10 +425,7 @@ func (sq *SearchQuery) Unmarshal(src []byte) ([]byte, error) {
 		src = tail
 
 		tagFilters := sq.TagFilterss[i]
-		if n := int(tfsCount) - cap(tagFilters); n > 0 {
+		tagFilters = slicesutil.SetLength(tagFilters, int(tfsCount))
-			tagFilters = append(tagFilters[:cap(tagFilters)], make([]TagFilter, n)...)
-		}
-		tagFilters = tagFilters[:tfsCount]
 		for j := 0; j < int(tfsCount); j++ {
 			tail, err := tagFilters[j].Unmarshal(src)
 			if err != nil {

lib/storage/table_search.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/fasttime"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 )
 
 // tableSearch performs searches in the table.
@@ -84,10 +85,7 @@ func (ts *tableSearch) Init(tb *table, tsids []TSID, tr TimeRange) {
 	ts.ptws = tb.GetPartitions(ts.ptws[:0])
 
 	// Initialize the ptsPool.
-	if n := len(ts.ptws) - cap(ts.ptsPool); n > 0 {
+	ts.ptsPool = slicesutil.SetLength(ts.ptsPool, len(ts.ptws))
-		ts.ptsPool = append(ts.ptsPool[:cap(ts.ptsPool)], make([]partitionSearch, n)...)
-	}
-	ts.ptsPool = ts.ptsPool[:len(ts.ptws)]
 	for i, ptw := range ts.ptws {
 		ts.ptsPool[i].Init(ptw.pt, tsids, tr)
 	}

lib/uint64set/uint64set.go

@@ -6,6 +6,8 @@ import (
 	"sync"
 	"sync/atomic"
 	"unsafe"
+
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/slicesutil"
 )
 
 // Set is a fast set for uint64.
@@ -226,11 +228,9 @@ func (s *Set) AppendTo(dst []uint64) []uint64 {
 	}
 
 	// pre-allocate memory for dst
-	dstLen := len(dst)
+	sLen := s.Len()
-	if n := s.Len() - cap(dst) + dstLen; n > 0 {
+	dst = slicesutil.ExtendCapacity(dst, sLen)
-		dst = append(dst[:cap(dst)], make([]uint64, n)...)
+
-		dst = dst[:dstLen]
-	}
 	s.sort()
 	for i := range s.buckets {
 		dst = s.buckets[i].appendTo(dst)