func NewBuilder(base Labels) *Builder {
	return &Builder{
		base: base,
		del:  make([]string, 0, 5),
		add:  make([]Label, 0, 5),
	}
}
NewBuilder returns a new LabelsBuilder
package labels
import (
	"bytes"
	"encoding/json"
	"sort"
	"strconv"
	"strings"
	"github.com/cespare/xxhash"
)
const sep = '\xff'
const (
	MetricName   = "__name__"
	AlertName    = "alertname"
	BucketLabel  = "le"
	InstanceName = "instance"
)
type Label struct {
	Name, Value string
}
type Labels []Label
func (ls Labels) Len() int           { return len(ls) }
func (ls Labels) Swap(i, j int)      { ls[i], ls[j] = ls[j], ls[i] }
func (ls Labels) Less(i, j int) bool { return ls[i].Name < ls[j].Name }
func (ls Labels) String() string {
	var b bytes.Buffer
	b.WriteByte('{')
	for i, l := range ls {
		if i > 0 {
			b.WriteByte(',')
			b.WriteByte(' ')
		}
		b.WriteString(l.Name)
		b.WriteByte('=')
		b.WriteString(strconv.Quote(l.Value))
	}
	b.WriteByte('}')
	return b.String()
}
func (ls Labels) MarshalJSON() ([]byte, error) {
	return json.Marshal(ls.Map())
}
func (ls *Labels) UnmarshalJSON(b []byte) error {
	var m map[string]string
	if err := json.Unmarshal(b, &m); err != nil {
		return err
	}
	*ls = FromMap(m)
	return nil
}
func (ls Labels) Hash() uint64 {
	b := make([]byte, 0, 1024)
	for _, v := range ls {
		b = append(b, v.Name...)
		b = append(b, sep)
		b = append(b, v.Value...)
		b = append(b, sep)
	}
	return xxhash.Sum64(b)
}
func (ls Labels) Copy() Labels {
	res := make(Labels, len(ls))
	copy(res, ls)
	return res
}
func (ls Labels) Get(name string) string {
	for _, l := range ls {
		if l.Name == name {
			return l.Value
		}
	}
	return ""
}
func (ls Labels) Has(name string) bool {
	for _, l := range ls {
		if l.Name == name {
			return true
		}
	}
	return false
}
func Equal(ls, o Labels) bool {
	if len(ls) != len(o) {
		return false
	}
	for i, l := range ls {
		if l.Name != o[i].Name || l.Value != o[i].Value {
			return false
		}
	}
	return true
}
func (ls Labels) Map() map[string]string {
	m := make(map[string]string, len(ls))
	for _, l := range ls {
		m[l.Name] = l.Value
	}
	return m
}
func New(ls ...Label) Labels {
	set := make(Labels, 0, len(ls))
	for _, l := range ls {
		set = append(set, l)
	}
	sort.Sort(set)
	return set
}
func FromMap(m map[string]string) Labels {
	l := make([]Label, 0, len(m))
	for k, v := range m {
		l = append(l, Label{Name: k, Value: v})
	}
	return New(l...)
}
func FromStrings(ss ...string) Labels {
	if len(ss)%2 != 0 {
		panic("invalid number of strings")
	}
	var res Labels
	for i := 0; i < len(ss); i += 2 {
		res = append(res, Label{Name: ss[i], Value: ss[i+1]})
	}
	sort.Sort(res)
	return res
}
func Compare(a, b Labels) int {
	l := len(a)
	if len(b) < l {
		l = len(b)
	}
	for i := 0; i < l; i++ {
		if d := strings.Compare(a[i].Name, b[i].Name); d != 0 {
			return d
		}
		if d := strings.Compare(a[i].Value, b[i].Value); d != 0 {
			return d
		}
	}
	return len(a) - len(b)
}
type Builder struct {
	base Labels
	del  []string
	add  []Label
}