Use iter.Seq, added in Go 1.23 (#49)

First-class support for custom iterators was added in Go 1.23.
Use that as a mechanism for iterating over Pointer tokens.

Also, update the workflows to test on Go 1.23
and bump the go.mod language version to 1.23.

.github/workflows/test.yml

@@ -9,7 +9,7 @@ jobs:
     - name: Install Go
       uses: actions/setup-go@v5
       with:
-        go-version: 1.22.x
+        go-version: 1.23.x
     - name: Checkout code
       uses: actions/checkout@v4
     - name: Test
@@ -23,7 +23,7 @@ jobs:
   test-all:
     strategy:
       matrix:
-        go-version: [1.22.x]
+        go-version: [1.23.x]
         os: [ubuntu-latest, macos-latest, windows-latest]
     runs-on: ${{ matrix.os }}
     steps:

go.mod

@@ -3,4 +3,4 @@
 // This package will regularly experience breaking changes.
 module github.com/go-json-experiment/json
 
-go 1.22
+go 1.23

jsontext/state.go

@@ -5,6 +5,7 @@
 package jsontext
 
 import (
+	"iter"
 	"math"
 	"strconv"
 	"strings"
@@ -51,20 +52,37 @@ func (s *state) reset() {
 
 // Pointer is a JSON Pointer (RFC 6901) that references a particular JSON value
 // relative to the root of the top-level JSON value.
+//
+// There is exactly one representation of a pointer to a particular value,
+// so comparability of Pointer values is equivalent to checking whether
+// they both point to the exact same value.
 type Pointer string
 
-// nextToken returns the next token in the pointer, reducing the length of p.
-func (p *Pointer) nextToken() (token string) {
-	*p = Pointer(strings.TrimPrefix(string(*p), "/"))
-	i := min(uint(strings.IndexByte(string(*p), '/')), uint(len(*p)))
-	token = string(*p)[:i]
-	*p = (*p)[i:]
-	if strings.Contains(token, "~") {
-		// Per RFC 6901, section 3, unescape '~' and '/' characters.
-		token = strings.ReplaceAll(token, "~1", "/")
-		token = strings.ReplaceAll(token, "~0", "~")
-	}
-	return token
+// Tokens returns an iterator over the reference tokens in the JSON pointer,
+// starting from the first token until the last token (unless stopped early).
+//
+// A token is either a JSON object name or an index to a JSON array element
+// encoded as a base-10 integer value.
+// It is impossible to distinguish between an array index and an object name
+// (that happens to be an base-10 encoded integer) without also knowing
+// the structure of the top-level JSON value that the pointer refers to.
+func (p Pointer) Tokens() iter.Seq[string] {
+	return func(yield func(string) bool) {
+		for len(p) > 0 {
+			p = Pointer(strings.TrimPrefix(string(p), "/"))
+			i := min(uint(strings.IndexByte(string(p), '/')), uint(len(p)))
+			token := string(p)[:i]
+			p = p[i:]
+			if strings.Contains(token, "~") {
+				// Per RFC 6901, section 3, unescape '~' and '/' characters.
+				token = strings.ReplaceAll(token, "~1", "/")
+				token = strings.ReplaceAll(token, "~0", "~")
+			}
+			if !yield(token) {
+				return
+			}
+		}
+	}
 }
 
 // appendStackPointer appends a JSON Pointer (RFC 6901) to the current value.

jsontext/state_test.go

@@ -7,10 +7,32 @@ package jsontext
 import (
 	"fmt"
 	"reflect"
+	"slices"
 	"strings"
 	"testing"
 )
 
+func TestPointerTokens(t *testing.T) {
+	tests := []struct {
+		in   Pointer
+		want []string
+	}{
+		{in: "", want: nil},
+		{in: "a", want: []string{"a"}},
+		{in: "~", want: []string{"~"}},
+		{in: "/a", want: []string{"a"}},
+		{in: "/foo/bar", want: []string{"foo", "bar"}},
+		{in: "///", want: []string{"", "", ""}},
+		{in: "/~0~1", want: []string{"~/"}},
+	}
+	for _, tt := range tests {
+		got := slices.Collect(tt.in.Tokens())
+		if !slices.Equal(got, tt.want) {
+			t.Errorf("Pointer(%q).Tokens = %q, want %q", tt.in, got, tt.want)
+		}
+	}
+}
+
 func TestStateMachine(t *testing.T) {
 	// To test a state machine, we pass an ordered sequence of operations and
 	// check whether the current state is as expected.