Update minimal go version to 1.18

Upgrading to 1.18 allows the package to rely on generic implementations
of its internal stack and queue data structures.

.github/workflows/go.yml

@@ -14,7 +14,7 @@ jobs:
 
     strategy:
       matrix:
-        go-version: [ '1.16', '1.21', '1.22.x' ]
+        go-version: [ '1.18', '1.21', '1.22.x' ]
 
     steps:
       - uses: actions/checkout@v4

etree.go

@@ -13,7 +13,7 @@ import (
 	"errors"
 	"io"
 	"os"
-	"sort"
+	"slices"
 	"strings"
 )
 
@@ -858,12 +858,12 @@ func (e *Element) RemoveChildAt(index int) Token {
 
 // autoClose analyzes the stack's top element and the current token to decide
 // whether the top element should be closed.
-func (e *Element) autoClose(stack *stack, t xml.Token, tags []string) {
+func (e *Element) autoClose(stack *stack[*Element], t xml.Token, tags []string) {
 	if stack.empty() {
 		return
 	}
 
-	top := stack.peek().(*Element)
+	top := stack.peek()
 
 	for _, tag := range tags {
 		if strings.EqualFold(tag, top.FullTag()) {
@@ -891,7 +891,7 @@ func (e *Element) readFrom(ri io.Reader, settings ReadSettings) (n int64, err er
 
 	dec := newDecoder(r, settings)
 
-	var stack stack
+	var stack stack[*Element]
 	stack.push(e)
 	for {
 		if pr != nil {
@@ -916,7 +916,7 @@ func (e *Element) readFrom(ri io.Reader, settings ReadSettings) (n int64, err er
 			return r.Bytes(), ErrXML
 		}
 
-		top := stack.peek().(*Element)
+		top := stack.peek()
 
 		switch t := t.(type) {
 		case xml.StartElement:
@@ -1411,25 +1411,12 @@ func (e *Element) RemoveAttr(key string) *Attr {
 
 // SortAttrs sorts this element's attributes lexicographically by key.
 func (e *Element) SortAttrs() {
-	sort.Sort(byAttr(e.Attr))
-}
-
-type byAttr []Attr
-
-func (a byAttr) Len() int {
-	return len(a)
-}
-
-func (a byAttr) Swap(i, j int) {
-	a[i], a[j] = a[j], a[i]
-}
-
-func (a byAttr) Less(i, j int) bool {
-	sp := strings.Compare(a[i].Space, a[j].Space)
-	if sp == 0 {
-		return strings.Compare(a[i].Key, a[j].Key) < 0
-	}
-	return sp < 0
+	slices.SortFunc(e.Attr, func(a, b Attr) int {
+		if v := strings.Compare(a.Space, b.Space); v != 0 {
+			return v
+		}
+		return strings.Compare(a.Key, b.Key)
+	})
 }
 
 // FullKey returns this attribute's complete key, including namespace prefix

go.mod

@@ -1,3 +1,3 @@
 module github.com/beevik/etree
 
-go 1.16
+go 1.18

helpers.go

@@ -10,37 +10,36 @@ import (
 	"unicode/utf8"
 )
 
-// A simple stack
-type stack struct {
-	data []interface{}
+type stack[E any] struct {
+	data []E
 }
 
-func (s *stack) empty() bool {
+func (s *stack[E]) empty() bool {
 	return len(s.data) == 0
 }
 
-func (s *stack) push(value interface{}) {
+func (s *stack[E]) push(value E) {
 	s.data = append(s.data, value)
 }
 
-func (s *stack) pop() interface{} {
+func (s *stack[E]) pop() E {
 	value := s.data[len(s.data)-1]
-	s.data[len(s.data)-1] = nil
+	var empty E
+	s.data[len(s.data)-1] = empty
 	s.data = s.data[:len(s.data)-1]
 	return value
 }
 
-func (s *stack) peek() interface{} {
+func (s *stack[E]) peek() E {
 	return s.data[len(s.data)-1]
 }
 
-// A fifo is a simple first-in-first-out queue.
-type fifo struct {
-	data       []interface{}
+type queue[E any] struct {
+	data       []E
 	head, tail int
 }
 
-func (f *fifo) add(value interface{}) {
+func (f *queue[E]) add(value E) {
 	if f.len()+1 >= len(f.data) {
 		f.grow()
 	}
@@ -50,33 +49,34 @@ func (f *fifo) add(value interface{}) {
 	}
 }
 
-func (f *fifo) remove() interface{} {
+func (f *queue[E]) remove() E {
 	value := f.data[f.head]
-	f.data[f.head] = nil
+	var empty E
+	f.data[f.head] = empty
 	if f.head++; f.head == len(f.data) {
 		f.head = 0
 	}
 	return value
 }
 
-func (f *fifo) len() int {
+func (f *queue[E]) len() int {
 	if f.tail >= f.head {
 		return f.tail - f.head
 	}
 	return len(f.data) - f.head + f.tail
 }
 
-func (f *fifo) grow() {
+func (f *queue[E]) grow() {
 	c := len(f.data) * 2
 	if c == 0 {
 		c = 4
 	}
-	buf, count := make([]interface{}, c), f.len()
+	buf, count := make([]E, c), f.len()
 	if f.tail >= f.head {
-		copy(buf[0:count], f.data[f.head:f.tail])
+		copy(buf[:count], f.data[f.head:f.tail])
 	} else {
 		hindex := len(f.data) - f.head
-		copy(buf[0:hindex], f.data[f.head:])
+		copy(buf[:hindex], f.data[f.head:])
 		copy(buf[hindex:count], f.data[:f.tail])
 	}
 	f.data, f.head, f.tail = buf, 0, count

path.go

@@ -152,7 +152,7 @@ type filter interface {
 // a Path object.  It collects and deduplicates all elements matching
 // the path query.
 type pather struct {
-	queue      fifo
+	queue      queue[node]
 	results    []*Element
 	inResults  map[*Element]bool
 	candidates []*Element
@@ -180,7 +180,7 @@ func newPather() *pather {
 // and filters.
 func (p *pather) traverse(e *Element, path Path) []*Element {
 	for p.queue.add(node{e, path.segments}); p.queue.len() > 0; {
-		p.eval(p.queue.remove().(node))
+		p.eval(p.queue.remove())
 	}
 	return p.results
 }
@@ -406,9 +406,9 @@ func (s *selectChildren) apply(e *Element, p *pather) {
 type selectDescendants struct{}
 
 func (s *selectDescendants) apply(e *Element, p *pather) {
-	var queue fifo
+	var queue queue[*Element]
 	for queue.add(e); queue.len() > 0; {
-		e := queue.remove().(*Element)
+		e := queue.remove()
 		p.candidates = append(p.candidates, e)
 		for _, c := range e.Child {
 			if c, ok := c.(*Element); ok {